Marion, I'm not sure what blues lick you're referring to. In general, though, blues guitarists have played on steel strings, and the techniques they have developed were worked out on steel strings. So what you say doesn't surprise me. If you're trying to bend strings, for instance (common in blues guitar, as I'm sure you know), you will find the result considerably less satisfying on nylon strings -- it can be done, and may even result in a pleasing effect, but it is a fundamentally different effect than you'll get from steel strings.

Again, it's a different instrument - so as long as you know that going in (it sounds like you do), you'll probably figure things out just fine. Have fun.