Developers who use the user agent string should be sho... well, ehm... should undergo educational correction. Unfortunately the average developer is just that: average. And judging by the quality of many websites, that's not something to be proud of.

But ironically, the arrival (or return) of internet explorer in Windows Phone might help the situation. It is a different engine which, from what I understand, does a remarkable job in standards compliance. Also, Google has forked webkit. So now we have three more or less different engines, which are all quite capable of handling the standards. It might push developers in developing for standards, instead of focusing only on a single engine.

But old habits die hard. Point in case: flash video. Every browser today supports HTML5 video. It really isn't that hard to use it, and to provide truly cross platform videos on desktop and mobile. I've done it myself, and it works even on the default browser on the N9. Still, even new sites use flash-based crap for their videos.