Are you sure the people who say the former aren't saying it in a light-hearted jokey trying to lighten the situation up a bit sort of way? I know tons of parents who joke about how they were waiting for their kids to start talking (because of course everyone wants their kids to talk and communicate and all) but now "wish they never did, because they don't stop!" and whatnot. It's just something people joke about. I really do not think they are trying to be rude or insensitive, but just trying to lighten your worries with a little humor. I think the best way to let it roll off is to simply remember that, they're trying to cheer you up about it, not offend you. It might also help you and them, if you could politely tell them, I understand you're joking, but my child is truly delayed, so I'm sorry but I don't think that is very appropriate to say under the circumstances. I'm sure if you said that they would be apologizing and saying they didn't realize and mean anything bad by it, and then they'll know for the future.
As for the actual speech, how many months is your child? I worked as a nanny and in a daycare, 6 yrs professional experience, and I can tell you, from the hundreds of children I have worked with, that everyone starts at their own pace. One little girl (who is now 6.5yrs) pretty much hadn't uttered a single word at 18 mos, and continued simply not speaking until she turned 2. At which point it was like she had been listening all that time and storing everything up, and then she just started talking and she really did never stop! haha. Her speech simply took off like a rocket and she never looked back! Quite different than the average child who slowly accumulates and repeats and everything. Anyway, just one example. But really, they all start in their own time. There's certainly no harm in pursuing help though, especially if professionals agree that she may benefit from it. As long as it's done properly and not trying to force anything, but encouraging it in a more structured way, then it can only help, right? =) I'm sure she'll get there.