I'd disagree with that actually. Good quality EF-S lenses will hold their value especially if you buy them
second hand. I'm sure you could buy any of the decent 17-xx lenses (or the 15-85)
second hand and lose next to nothing when/if you sell them. If you end up with 2 bodies - one crop, the other full frame - then you're probably going to want to keep a good quality EF-S lens anyway to get the most bang for buck. If you're not, buy second hand and sell on.
Certainly, I can't imagine owning two EF lenses to keep on the two cameras for walkabout. I'd end up with a 24-70 and a 24-105 so that one would be on the 7D when the other is on the 5D2. That would be expensive on one hand and on the other, I'd need a 10-22 (ish) for the 7D as 24mm wouldn't be wide enough for me on crop. Yet another EF-S lens to buy as the 17-40 would just be too frustrating on crop (not very wide, not very long)...
No. Does yours make mine any less valid?