The blown diffuser was a special case that was corner dependent.
The cars are not evenly matched, I have no idea where people are getting this from. Look at the race yesterday- Button the guy that won the first race was nearly lapped. Rosberg who beat Maldonado by 30's two races ago finished 78s behind him yesterday. Barcelona is usually viewed as the real test of a car's WCC/WDC potential so I guess we can take it that Williams have now the best car in F1(probably by a big margin as I doubt Maldonado is in Alonso's league).
The drivers and teams haven't been too vocal about it probably because most of them are happy to be in the mix for wins/podiums. However fans of the sport, and no offence but most people here are probably just casual F1 fans, are starting to get very vocal about the farce that is unfolding.
I'd say I'm anything but a casual F1 fan - I've not missed a race since 1982 and even spend my weekends racing myself. Contrary to what you say, I actually am very happy with way F1 is this year - including the tyres.
Making those comparisons of the gaps between certain cars at different races doesn't work. There are many factors involved that contribute to those differences (not just the tyres) including but not limited to - Aerodynamic updates, Circuit characteristics, Driver (good or bad day), Setup, Temperature etc. The gaps are also exacerbated by the fact that the leader get the benefit of running in clear air, unhindered on a near optimal strategy, where anyone in the pack will lose time which is compounded by lost time defending, following slower cars, racing wheel to wheel, increased tyre degredation and sub optimal strategies designed to give track position.
You can only really make the comparison above if drivers were each to set their race time on an empty circuit!
This year all of the top teams are very very close with no more than about a second per lap between them in the raw perfomance of the cars. This is due to the long period of stability in the rules and banning of the complex to develop systems such as blown diffusers that only the richest teams could afford to optimise.
F1 cars are complex machines to set up - they are by nature super-optimised pieces of machinery and as a result the window of operation is small. Get it just slightly wrong and you can easily have a performance swing of a few tenths to a half second either way.
In the past this was less of an issue. The top teams were a second or two clear of the rest of the pack - so even when they got it wrong, they'd still qualify on the front 3 rows. That is the reason why racing used to be more predictable and it has little to do with the tyres.
This year, whichever team brings a car that suits the circuit, gets the setup and strategy right and has a driver who is hooked up has a serious shot at winning the race as the tenths gained from each of those actions are enough to take them from the back to the front of the grid in qualifying because it the cars as so close in base performance.
A good example of this is comparing how one team mate can look a hero where the other is struggling well out of the points. EG Bruno and Pastor in spain or Alonso and Massa all year. Just a few tenths difference in the critical phases of qualifying being the difference between a front row grid spot and 16th or 17th. In the race as mentioned above, this difference is then compounded by running in traffic etc leaving the drivers almost a lap apart at the end of the race. It's the same car and the same tyres - so I think it's fair to say that the tyres are not the cause of this "lottery" that you are complaining about so much.
The tyres do obviously make some difference - having new tyres with relatively high degredation and relatively small operating windows means that the teams aren't 100% on top of them yet. But importantly - the tyres are the same for everyone so whichever team and driver combination does the best job on a race weekend has a shot of winning. Surely that is exactly what F1 should be about?
Having read some of the arguments on the autosport forums regarding this subject, you can't help from feel that a lot of the bitterness towards pirelli is discomfort that peoples favoured drivers are being beaten by "rubbish midfielders" like Maldonado, Perez, Grosjean etc. What I don't think most people appreciate is that at this level the drivers are much closer in ability than they would like to believe. There is barely more than a few tenths on average in pure pace between the very best and the worst on the grid - in the past car performance differences have flattered the "quick" drivers more than is fair. This year we may actually get a chance to see just how good some of the other drivers in smaller teams are too.
The beauty of all this however is that the best drivers will rise to the top because they will be the ones who can more consistently peform at a higher level - Alonso and Vettel being a prime examples so far this season.
Fundamentally - that is the kind of F1 I like to see - where the best drivers can make a real difference over the season instead of much of the previous iteration of F1 with durable tyres and fuel stops where the car was overwhelmingly the biggest determinant of who would win the championship.
One last thing to mention is all the nonsense about drivers having to manage their tyres over a race distance "not being what F1 is about" because certainly in the vast majority of F1 history that's always been a absolute key element to the racing.