I think the real reason new technologies appear on HP9000's far in
advance of 3000's is competition.  Since you can buy a Unix box from
any of several vendors, and the (substantially incorrect) belief is that
Unix is the same on all platforms, the various vendors differentiate
themselves on the basis of price/performance and the latest technological
goodies.  No vendor can afford to be too far off the leading edge in terms
of technology.  The HP3000, on the other hand, is sold on the basis of its
OS, and its reliability, ease of use, etc.  An MPE customer isn't going to
jump ship to get the latest gadget from another vendor, because the cost
and lead time of converting to another OS is prohibitive.  HP can take a
more leisurely pace, they believe, without losing business to other
vendors.

As stated by others, there are other factors, such as the size of the
installed base and ease of implementation.  Still, to the extent that HP
regards the 3000 product line as less urgent, I believe they lose sight of
the impact of those decisions on potential customers' perception of HP's
commitment to the platform.