While I don't think it would have been enough to make a measurable difference in the collapse speed -(I think the collapse should have eventually
halted, but not necessarily suddenly so at the mechanical floors), the mechanical floors were in fact stronger in certain design aspects.
* At the mechanical floors, the exterior columns were spliced at the same level rather than being staggered like the other floors. Supplementary welds
were added to increase rigidity.
* There was additional diagonal bracing in the core area of the mechanical floors and as part of the hat truss. There are pics taken at the time of
construction showing this if you do a search.
* The composite floors of the mechanical floors were framed with wide-flange structural steel beams rather than the thin, fluted metal deck and
lightweight trusses of the other floors.
* Some floors adjacent to the mechanical floors used a hybrid of steel beam and truss framing acting compositely with the concrete slab.
The lower live load design ratings for the mechanical floors (75psf compared to 100psf) was simply because those floors experienced less load. The odd
machinery and equipment isn't going to create as much load as hundreds of people, paper, office equipment and furniture.
This is all in the NIST reports and fairly common knowledge to those who have spent any time really looking at this aspect of 9-11.
But as I said, isn't this thread about WTC7? Besides, WTC1 & 2 have been done to death.
EDIT: Just saw your post after I posted mine, Skibum:
My apologies, its hard to keep track sometimes.
Will get back on track now.
No worries, it happens to all 9-11 threads. Wait until the Pentagon gets brought into this one.

lol...
[edit on 2006-5-1 by wecomeinpeace]