I really dont understand where you get all your probably logic from tbh, I may be wrong here but I dont think the 1 year extension comes into effect the minute a player turns 30, maybe 32/33 but Berbatov has only just turned 30
because its well known that Fergie wants more young blood in the team, and apart from Giggs (who isnt likely to go anywhere, and cost nothing to start wtih) - and Scholes who looks likely to retire for right or wrong - yes I do believe as soon as any player hits 30 , the next round of "negotiating" will be regarding 1 year ext rather than multi year ones
Rio's 5 year deal was signed just before he was 30 in 2008 I believe (but might have been a special case due to being on field captain and SAF/Gill probably knew he would be club captain shortly.)
In Berba's case, seening as he is blatantly 3rd choice striker, only had one very successful seasons so far at Utd, and possibly wanting 100k/week or more , I dont know whether it makes financial sense to sign a multi -year deal anyway (from club's point of view).
Personally if its a choice between Berba's wages or a 10-15 goal a season AM or left winger (and Berba's £10m-£15m transfer) I would choose latter every day of the week
In games where Rooney and Berbatov have played together the latter has scored 3 goals against Liverpool, 5 against Blackburn and 3 against Birmingham among others. Not sure how you've come to the conclusion that the team plays better without Berbatov in the starting XI
And lets totally forget all the matches Berba has cost Utd the game by misfiring or not turning up - he blatantly isnt reliable enough
He may score loads when he does score, but its never been consistant goals (for Utd at least) which is what his wages should be getting
edit - even in Giggs' wiki entry it says the below:
"Since 2006 After that season, Giggs signed a two-year contract extension with United
when chief executive David Gill relented on his normal policy of not signing players over 30 to contracts longer than one year."
Now whether Utd plan the players previous contract to run out as near to their 31th birthday (so all re-negotiating happens around their 30th, for any potential transfer fee just in case) I have no way of knowing, but it certainly makes perfect business sense to do so where possible (given the policy stated at the club)