If they really wanted to fix this, the text would read "How many rides would you like to purchase ($2.50 per ride)". Of course, this only works if every ride is $2.50.
Oh, and if you want a plastic RFID card rather than magnetic paper that will fall apart within 3 trips, you need to spend $10 for $8 of fare. (EDIT: And another commenter mentioned something I'd forgotten: those paper farecards also come with a $1 surcharge per trip.)
http://wamu.org/news/10/10/15/metro_board_replacing_smartrip...