Cant speak for anyone else, but my general feeling is they do listen to feedback - good and bad - and as you can see - they even frequent many forums and engage in discussion (marc works for access even if he doesnt obviously say so)
As for the synth being the best it can be - on balance - it probably is, else so many wouldnt be using as their primary synth. In my case - I have a whole heap of synths, but TBH the TI get about 95 of the work, while the other 10 or so get the remainder. Im sure many people can find fault with some design choices (I can in the context of how I personally want to use it at times, but I still maintain there is nothing else on the market that is as useful, or sounds as good for such a broad palette of sounds), but they cant implement everything that everyone asks for.
I guess the other biggy for access is they have a history of giving very major free updates through the product cycle - OS v2.x for eg has added a whole heap of new synthesis types - for some of us thats as good as having a completely new synth, but without the usual learning curve.
Also the nature of internet forums are alot of folks come looking for help with issues, which tend to skew them very much towards negative posts compared to the community experience as a whole. and to be balanced - Ive had some major problems with the TI back in its early days, these days however its very reliable using it standalone, in ableton live and in cubase 4.