I had a good laugh too, wow, but the engineer in me found it a bit hard to accept a strong relationship between the 12-foot diameter (see http://www.thiokol.com/Space/RSRM.htm) of the space shuttle SRB sections shipped by rail and the 4'8.5" standard gauge. For other anal retentives, here's the best serious discussion that I could find on the net, amongst the hundreds of regurgitations of the urban-myth-cum-joke:
http://www.straightdope.com/columns/000218.html

Cheers,
Marty. B.E.(Mech) and B.PartyPooping (Hons) ['trying not to take my profession too seriously' emoticon]