Amps on top?

Steel tends to sing (vibrations at a particular frequency). Its a thing so hopefully your off road truck friend was able to mitigate that during construction. Best.

This high end  fellow I know has a huge old heavy very thick solid cherry bookcase cabinet modified for a large screen in center, four monoblocks in it at bottom center.  A pre pro, two Richard grey power centers there 220 volt. At the very top left and right hand corners about 7' off floor are two monoblocks German high end amps 220 volt I believe or two cords on each. Before this he had his arc 750's up there. Also a high end turntable was in there. His ancillary gear is in a rack on left of room.  No room treatments whatsoever. 18 by 18' 12' ceiling.  Two huge JL audio subs sit next to cabinet, two huge base towers and tweeter towers out front. He had 5 dacs, the best being  a Berkeley ref 3.  Damndest thing you ever seen.  

Is there any other reason appart from weight and speaker cable length?

@ghasley I designed the stand.   I've been working in an industry dealing with vibrations for over 40 years.  I know those selling other things have talked down steel and many have read their marketing.  I wish them luck. 

Jerry

I hit the lottery and bought a used BDI rack for $100.     It is heavy gauge steel and Birch ply.    It is strong.   I have my tube amp on the top shelf ,  plenty of space around it.   Preamp is below , with a shelf removed so it has plenty of space to breath too.  DAC, tuner , streamer are all on separate shelves.    Everything stays cool,  as cool as tubes can be I guess