Certainly seems that way. Above you can see the AT&T download site where BlackBerry Desktop Manager is to be downloaded for AT&T customers. This list, not too long ago was filled with versions as far back as 4.0 but no longer offers anything less then 4.6. Now while some might just say that's just AT&T pulling them off of there to avoid confusion the same thing can be witnessed across multiple carriers.
Even the Research In Motion website has abolished all versions except for 5.0 iterations on their download page. I'm quite certain this is nothing more than just a little bit of house cleaning, but it was rather surprising to see for the first time. It should help some folks out, that's for sure. Rather then 10 different items users nowhave less chances of downloading an incompatible version.
[ Hat tip to Banthon ]