Well, I'm not sure what specifically he was trying to explain, but he clearly didn't know what he was talking about. It is ridiculous to think that any commercially available cell phone would effectively make purchases without authorization, and I have never heard of any Treo doing anything like that. My guess is that he is "prejudiced" against Palm OS, either because the 700w might be higher margin, or maybe he is just one of those M$ zealots who thinks that anything other than Microsoft must be bad. Maybe try a different store?
Perhaps he was thinking about an e-mail program checking for e-mail automatically, even if you don't have a data plan...? And it's not like you could just not enter any e-mail accounts or something...
EDIT: Since maybe some people here don't appreciate my brand of, um, sarcasm, the above was my cynical way of saying that a Treo can't possible automatically check e-mail if you don't want it to, since you could simply not enter any e-mail information. It might have a Verizon e-mail account pre-programmed, but if so, I would certainly hope you could delete it.