I think it's awfully stingy, and if it were me, I'd ask them about it, gently. Just tell them you'd love to take the job, but you have just one concern. Tell them you're accustomed to more vacation/personal/sick time and ask if there is any way that you can be given more. The worst they can do is say no, but they're not going to withdraw the job offer for asking nicely. I wouldn't wait until after you've accepted the offer, that'd be too late.
I did this once, with a job where the vacation time was better than you've described, but still less that I was accustomed to. Although they couldn't do anything about it from an HR standpoint, the head of the department realized that she'd have trouble hiring people who could get better benefits elsewhere, so they gave us extra days off that they tracked at the department level. Now, I'm not saying for sure you'll get something like this, but you never know unless you ask, right?
Even if you can't get any additional time, go ahead and take the job. You can keep looking for another. Good luck.