I'm not sure how accurate the chewing/speech development thing is - I would suspect, as with all things, that it is not as simple as that, and that there are many other variables involved! The theory, I believe, is that if babies don't have to chew, their oral muscles don't develop so well, but I would suggest that a direct link is tenuous because speech development isn't just about oral muscles and how strong they are!
Don't be phased, however, by the idea of introducing less than smooth purees - if you want your los to chew, offer some finger foods, there are some great ideas in the Finger Foods for Young Babies thread in the Recipes section - some parents find that their babies don't tolerate lumpy purees very well from a spoon, and actually transition better from smooth purees straight to finger foods - there's no reason that you can't be doing a combination of both right from the start if you want to!
Ax