Most writers link to Amazon or maybe Barnes and Noble so that visitors to their websites can click to buy their books. The thing I've noticed is that these websites usually only have those links, either one or the other or maybe both. There are a lot of websites that sell books. Why not create a clickable link to as many as possible?
Multitude Of Booksellers
Create links to Amazon, B&N Books, Alibris, Borders, Powell's Books, Better World Books, Books-A-Million, or any of the others. It's easy to find online booksellers with a search string. Don't forget to link to your local independent booksellers. They'll appreciate the boost.
While you're at it, be sure and link to your publisher's website where your book can also be purchased.
Leave no stone unturned in your marketing and promoting efforts.