Hmmm, well in my views. I'm still quite young and I'm still reasonably early into a relationship (just over a year) but if my partner said he didn't want kids I'd be gutted. We've talked about it a little, and he said we will in the future, but definitely not right now. (Although if you've seen some of my posts, you would know that I have had some cravings for a baby)
I don't think it's a case of not lack of commitment to you, just that they don't want the responsibilty of children. I find that a lot of men (and some women) just don't want to grow up, and as pea pod (I think was stating) would have to admit that they are getting older, and can't have the 'wild' lifestyle that they have or simply think they have.
But I guess it would depend on the couple on whether they could continue a long term relationship without children. If you simply couldn't bear the thought of not having children, then yes, eventually you'd have to either come to some kind of agreement, go seperate ways, etc.
I know many couples, older and younger who don't and haven't had children. Personally I find it sad that they haven't. But it's their choice at the end of the day.