One was basing the machine on PPC processors initially, because it limited their audience. I thought it was a cool idea, but wasn't willing to buy outdated hardware to get the OS. Mac users at the time could have simply acquired the OS and installed it, but the number of mac users willing to do that wouldn't ever be large.
One was not supporting IDE when they ported to x86. When they finally went after a large market, they made sure that hardly anyone in that market COULD use it. I had to do a lot of finagling with my computer in order to install BeOS on it.
AFAIK Apple actually DID try to buy Be before going after NeXT once they realized that Rhapsody simply wasn't going to happen. I've heard a number of stories regarding this, and I don't know which to believe; I was informed that the Be CEO rejected Apple's offer. If someone has better knowledge of that part of history than I and can confirm or correct me, that would be appreciated :)
BTW, where you wrote Rhapsody you meant Copland. NeXTSTEP was renamed to Rhapsody (and then OS X) after Apple bought it.
You're probably also right about the reason for starting out with a PPC based system. I'd heard about a similarly sized offer for Be, as well as JLG's refusal.
There weren't a lot of realtime OS's out there, and still aren't -- BeOS could have been the next OS/2, only without IBM's marketing behind it. (Can anyone say, "Friendly fire?")