One thing that bothers me, is that Dota 2 is still beta-invitational only. It's essentially closed beta with feedback forum up and running. Why would they need a test version if :
1. Current Dota 2 build has the option to run "tournament", i.e. if they need Dota 2 for public event they can run stable version no matter the latest patch.
2. Purpose of Beta is to test content, mechanics and servers.
If they wanted to lower the amount of people to just the devoted testers, then it might work, though I expect a lot of people switching for just the updates and not the testing.
1. The Tournament mode is just for 6.72f changes, rather than 6.73.
2. I think Valve is really pushing to make the current Dota 2 Beta a complete product, just without all the heroes at the moment. The quality of each the heroes in the updates has been very, very high so far. Also, I bet Valve has wasted quite a bit of time each Thursday trying to clear up massive issues with new heroes/bugs, that would be solved much easier with these widescale actual beta tests. This might mean more heroes can be shipped at once, rather than taking the risk of putting out 4 heroes at once to the current beta, they've got a good place to find and work out the kinks quickly. We'll see, though.