"My wife is a beta tester and is running 12-14 hours a day and the techs at the computer stores are stating that the external harddrives are meant for backups only and will not hold up to the constant access."

I think thats smoke.   

If she can use firewire try to get that - there was a big difference in loading speed for me.  Normally I don't say this about any computer hardware, but with ext drive you may want to get the store warranty in addition to whatever mfg one comes with it. 

I am:  aka Velocity3d