It's only fair. But actually, I should explain. I hate giving blowjobs. HATE. IT. Makes me want to cry and vomit all at the same time. However, if I couldn't have sex, I would be more than happy to give him a hand job, provided I get plenty of kissing time with him (of course, plenty of kissing time is a requirement for me in any intimate situation). And I give good hand jobs. When you spend years avoiding blowjobs, you get good at hand jobs. And before anyone asks -- No, I do not expect him to give me oral, ever. It's only fair, right?
So for the ladies who actually like giving blowjobs (how any woman could enjoy this is beyond me, but apparently such women do exist), they probably wouldn't mind doing it during their period. But for me, if it's that time of the month, I already feel like shit. I see no reason to do something that would make me feel even shittier. I certainly would not expect my bf to do anything that he hated. Especially during his period. :-)