The BBC still does produce a large amount of quality progamming, but budgets and purposes have been affected. Top Gear for example used to be about cars but is now an entertainment show - a wildly successful entertainment show, but no longer something you'd seriously watch to get an idea of what cars to buy and what to avoid. The BBC is also responsible for the One Show, which one day will be recognised by the UN as a crime against humanity. There's also been considerable dumbing down of shows like the Apprentice and Dragon's Den over time, eschewing quality in favour of personalities and entertainment. The natural history unit still put out good documentaries, but even they're not entirely untarnished[2].
The quality of news has also suffered, particularly thanks to spin doctors in previous administrations, the simon gilligan dodgy dossier affair and other stresses on the BBC. When was the last time you saw a proper debate? The other week I saw Alastair Campbell jogging around forests, talking up the end of civilisation through alcoholic poisoning brought on by drinking at home, demanding minimum pricing as the only way out but completely ignoring the impact of the smoking ban as a factor in home drinking increases. It was a terrible attempt at a documentary and a case study in what's wrong with the BBC at the moment.
I do apologise for getting on my soap box about this, you didn't deserve it for pointing out the good stuff. Still, the BBC is not a perfect organisation and the amount of media it has to produce combined with political interference has meant that quality has dropped, perhaps not as much considering the volume of material it puts out, but it isn't immune.
[1] - http://www.guardian.co.uk/commentisfree/2011/jun/08/today-pr...
[2] - http://www.telegraph.co.uk/culture/tvandradio/bbc/8950070/Fr...