Diagonals are hard to pull on arcade sticks?
I don't think so. There are generally different gates but most common is the square gates. You'll be able to 'feel' the corners a lot easier.
For a brief tutorial of the different types of arcade sticks there are, check out these articles:
http://shoryuken.com/forum/index.ph...read-the-guide-on-pg-1-before-posting.137321/
http://shoryuken.com/forum/index.php?threads/the-sanwa-and-seimitsu-faq.18346/