Look at it this way. The Alpha backers are used to getting multiple Gb updates over the course of a couple of days, with discussions along the line of 'is X.y+1 more unplayable than X.y'. Unleashing this sort of instability on the presumably significantly larger pool of Beta backers is silly. Beta backers for the most part will be expecting to be able to play without any blocking bugs.
All that has been revealed is that Alpha backers are being forced to Out-of-Box test the beta releases before the beta backers have to upgrade. I assume this isn't just for beta 1.0, but all incremental beta stages too.
I've clocked up a grand total of 321 minutes playing since Alpha3, mostly limited by my free time not aligning with the build at the time being stable enough. Exposing beta backers to the risk of new and exotic ways of getting persistent crash-to-desktop or worse is just madness.
The MP nature means that players have no choice about sticking with an older version - once a build is pushed out, it seems to be clear within hours if there is a big problem (and we've seen once or twice a new release pushed the same day to fix issues).