Of course not, because that would be annoying and unwieldy. On the other hand, you can add expansive dictionaries for every language to an ereader for the low, low weight of... nothing at all.

I suspect if you compare the usage of dictionaries among paper book readers vs ereader users, the latter use them more often - probably at least partially because they're so much easier to use. I suspect the incidence of not understanding a word would be pretty much the same.

For myself, I read a lot of older books with archaic and niche terms, so it's practically required to be able to look things up if I want to really understand what's going on.

(As an aside, I looked up a definition on Google just writing this to ensure I was using a word properly. :P)