Very interesting....I am surprised they don't advertise that when they are trying to get donations? Seems it would be good to put that on the page, at the very least it will generate some interest"What is bitcoin?"
Before they decided to accept BTC donations, Jimmy Wales (co-funder) was discussing the issue on reddit. And if I remember correctly, they had some concerns that some people who would normally send say $10 will send much smaller amount in bitcoins. Also, people who donate regularly could make payments less often after switching to BTC etc.
It's not completely unreasonable, I've seen many very small BTC charity donations (ie 0.001 = ~$0.37), if you use paypal/cc you probably won't send anything below $1 or even $5.
That's why wikimedia (and others) opt to 'hide' the BTC donation option.
