If Sony didn't want to deal with lenses that require a motor to drive them installed on the camera, then they shouldn't have bought Minolta, they should have started from scratch their own mount, maybe the E-mount would have arrived a long time ago.
But they didn't, they bought Minolta and they knew they were getting into a system that was mostly based on lenses driven by the camera, not a motor inside every lens. They picked up the ball, now they got to carry it.
The fact that Nikon made sure that you can't use their new lenses with old SLRs, doesn't mean Sony should do the same. I know plenty of photographers here who still use Nikon SLRs, but because of the lack of an aperture ring and that the old version of the mount won't drive the lens' motor, they can't use new lenses on their cameras.
Regardless of what companies think, SLRs are still used. So this dumb move by Sony of removing the focusing motor in the entry level bodies and installing electronic motors on the lenses so you won't complain about the noise they make during video recording, it's just doing what somebody already did. Minolta at least had the guts and vision to try new things and doing as much as possible to not make it backwards incompatible.
The only time they did, was when they switched the MD mount to AF, and that was because they didn't have another way out to make a mount with precise control over apertures, shutter speeds, etc. Canon ended up doing the same but it took them 2 years to catch up.
Taking in account that the current line-up has several holes filled by the Minolta glass that floats around, I find it foolish to remove the option of using legacy lenses on entry level bodies.
If Sony is that desperate for everyone to switch to SAM and SSM, they should lower their prices considerably, so the lenses are more affordable, but seeing that they raise them every 4 weeks, I really don't know where the hell they are aiming at.