I happen to know that they do this at the Linguistics Data Consortium (http://www.ldc.upenn.edu/), at least with cable news shows. They mostly do that to obtain data for languages with more minimal resources though, and for the purposes of transcription, not for speech recognition qua engineering research. The real issue though is the research community is interested in increasing the accuracy of recognizers on standard datasets by developing better models, not increasing accuracy per se. Having used more data isn't publishable. Further, in terms of real gains, the data is sparse (power law distributed), and so we need more than just a constant increase in the amount of data. This issue is general to any machine-learning scenario but is particularly pronounced in anything built on language.

Some related papers ~ Moore R K. 'There's no data like more data (but when will enough be enough?)', Proc. Inst. of Acoustics Workshop on Innovation in Speech Processing, IoA Proceedings vol.23, pt.3, pp.19-26, Stratford-upon-Avon, 2-3 April (2001). Charles Yang. Who's afraid of George Kingsley Zipf? Ms., University of Pennsylvania. http://www.ling.upenn.edu/~ycharles/papers/zipfnew.pdf