Never heard of speakers Dave? You use a screen reading program to read the page out loud to you. Images can't be read though, so the links are useless. Same with partially sighted people who would be using a high visibility browser, it shows only the text, so if the links are image, they can't be viewed.
There are a million analogies I could come up with, but websites are like any consumer product, you never know who is going to buy (or in this case, use) them, but is that any excuse for just aiming for the masses? You need to cater for everyone, and yes actually by law now believe it or not. If a blind or deaf person believes you are discriminating against them by not having your site accessible to them, they can take you to court over it. It's in the immensely interesting Disability Discrimination Act which I had to read for a presentation I did at uni. (Actually I met Harry on the back of that as well). All the cases have been dropped so far though because whenever it came up, the companies quickly sorted their sites out.
Interestingly, you can actually get a braille monitor. It puts pins up for each letter so you can read it as a printout.
Obviously a lot of design is subjective, but there are guidelines for best practice out there that have been approved by the RNIB (Royal National Institute for the Blind) and the DRC (Disability Rights Commission).
Anyway I'm done, as I've said before 99% of the site is fine, just the remaining 1% would stop any blind person from viewing it. This isn't new legislation either, it's been around since 2002.