Hmm...
Yes and no.
They certainly don't enable me to roleplay - one of my primary RP haunts is the MU* scene - the old talker systems that MMO's grew from and can't do any better than ASCII art and Pueblo image links. However, I will certainly admit that graphics can injure my ability to roleplay, if they're somehow offensive or incongruous .. and really nice graphics such as Final Fantasy XIV's do help a little.
I've never seen so perfect a rendition of Forra, I was actually a little shocked at how well it captured him .. seeing Forra right there almost exactly as I imagined him really does help, I admit.