In message , at 19:33:48 on Fri, 9 Sep
2011, tim.... remarked:
I think they believe the Heathrow Connect/HEx free shuttles fulfil that
need.

I think they do reasonably well, the only downside being the lower
frequency.

Quite a few people use the airside buses, which are rarer in the USA. I'd
like to say "unknown" but they do exist, I saw one at Newark last week
connecting Terminals A[1]&C (both of which have Continental flights).

I would have thought that the US policy of making everybody clear
immigration/customs at first entry point/final exit point restricts the
demand for air side transfers somewhat.

Not when the vast majority of transfers are domestic-domestic. Plus a
few domestic-international (I didn't clear security when transiting back
to UK through Newark, I stayed airside and the security I did earlier at
the regional feeder airport was sufficient).

It's only the international-domestic which have that issue.
--
Roland Perry