Your maths are wrong.
5% net interest of £20,000 is £1000 per year, which is a rather considerable sum.
Hahaha, how on earth did I screw that up so badly? That's gotta be my most embarrassing post ever (especially for an Economics & Maths graduate - just as well I don't work for the BoE eh!). I thought it seemed a bit low!
Looking at things on a more realistic scale, net savings rates have probably dropped by around 3% over the last year, so around £600/year worse off. I picked £20k just as a typical figure; obviously some may be saving up bigger deposits and be losing more in lost interest (but chances are if they have a lot more than £20k, they probably already have enough for a deposit on houses outside extreme regions anyway).
Meanwhile, over the past year average house prices have dropped from ~£190k to ~£157k (rough average of NW/Halifax figures for Dec07/08, with no account for volumes, so tilt the figures a little either way if you want). So in other words, a 10% deposit will now only be ~£15.7k, as opposed to ~£19k a year ago. To be conservative, lets say it's around a £3000 difference.
Now, due to changes in the market, a 10% deposit doesn't open up quite so many products as it once did. Lenders have also been increasing margins. But even so, due to the falling interest rate, the chances are you can get as good a deal today with a £15.7k deposit, as you could with a £19k deposit a year ago (even if it is no longer anywhere near market leading, and has a heftier arrangement fee attached).
So while I messed up with my figures, I still think my general view on deposits remains - they haven't suddenly got much harder to achieve. Plus a house bought for the average price used to come with an extra ~£1.9k of stamp duty - a house bought at the average price today has no stamp duty. Again, it depends on what sort of house you are after and where you live, I'm just talking averages here.