In analog NTSC, both broadcasters and cable operators have used the same modulation system. In the digital world, they're different. It does not require them to be turned back into either 8-VSB or analog signals. Despite the fact that virtually all analog television sets sold can tune cable channels, there were, indeed, some 8-VSB receivers sold that couldn't. The Houston Time Warner Cable system has taken the more common cable track, even though it prevents the receivers in integrated DTVs from being used.
More data means more channels.
According to the FCC, consumers are supposed to be able to buy those cable receivers in stores. Subscribers would be able to purchase set-top boxes in stores, and cable operators would then provide PODs for access control. That, at least, was the theory. They wanted security not just for conditional access but also for copy protection. They may allow no copying, single copies, unlimited copies, and more.