I have no doubt that this incident is true - Vai has
always stated - right from day one - that his number one priority with designing a guitar that he would endorse was to ensure that he could go into a guitar store and pick one up and play it and it would be what he wanted and expected...
However, there's lots and lots of info on Steve, his guitars and their history on
Jemsite if you want all the gory details (or as many as a bunch of Vai/Jem fanatics could dig up over 15 years of digging)...
There's a great deal of info on Steve's site as well in his
the Machines section - you might find one or two stock Jems in 120 some-odd guitars he has listed there... The vast majority are designated "prototype", "no serial number" or "one off" which means Ibanez gave 'em to him...