Why should you feel guilty? It's not like you're going to Vegas to party (and even if you were -- hey, we all need a break sometimes!)
If your husband does not mind being the main breadwinner so you don't have to work at all, then you won't have conferences to worry about in the first place.
Your husband, all due respect to your family, needs to man up a little. Not being there at night? Choosing work over family?? Oh please. It's called working for the betterment of your family in the midst of a recession. How about showing a little gratitude for the fact that your wife has a job at all, a gift during this recession? And while you are at it, some sympathy for a mother who will miss her dear children. It must be so hard to leave them.
I wonder what others will respond, but, if it helps, I bet that you are in the minority here. Never having spent more than one night away from your kids is pretty impressive so far, at least to me. I have gone a week or more away from my kid (3 years old) because of work or day care drama issues that have forced me to leave him with his grandparents at times. The fact that you are that close to them and that committed to always be present as a mother speaks volumes already. Good for you!
I think that your husband's attitude is not helping. Don't feel guilty; we all have to do what we need to do to support our families.