Bitcoin people are pretty eager to donate, because they want to support the currency. I developed a very small web site (https://cryptedmemo.com/), and have already received almost 2BTC donations. The site isn't even used that much.
I did /not/ downvote you (and still haven't), but honestly you may as well be suggesting he look into accepting contributions of ferrel camels on his website: 99.99% of people in the position to give you money at all are going to have bank accounts and cards, and are likely to have no clue how to even obtain bitcoin, much less actually own any; it simply isn't a realistic "option".
You make a fair enough point, the market size of bitcoin users is still very small. However, the technology it provides is real, and IMO, a valid solution to this problem. (even if it's not the only solution; it's not uncommon to accept multiple payment methods.)
Those that want to donate with bitcoin can easily google how to buy it, and will discover it's easier than ever to acquire. (in some cases, using paypal!)