However, 3rd party clients were the route into Twitter for a huge amount of early adopters (and even later adopters). Most Twitter "features" (including the retweet concept, hashtags an even the word "tweet") were from the open community they started with. Moreover, their own clients are falling behind even simple 3rd party experiences. Twitter for Mac has, essentially, been abandoned. How many users will swallow an inferior experience, just for the privilege of getting adverts thrust in?
For my 2p, I certainly won't - to me, the value of Twitter has been decreasing over time, not increasing. As it moves towards "mass market", it seems to be seeking a broadcast model, where billions of users subscribe to feeds of a few celebrities. It's becoming a "send only" service - the total amount of micro-conversions I've had in the last year is much lower than even 2 years ago.
Perhaps this will work out for them as a company - a real time newswire for companies and celebs to send 140 character press releases, interspersed with adverts. Or maybe I'm wrong, and mass adoption of their web and iffy mobile/desktop clients is coming. I just can't see it, yet.