I want to permanently get rid of unwanted apps in the store so my iPad won't reload them when I sinc. Can I do this?

You can't permanently delete any items from your purchase history, all you can do is hide them from the Purchased links so that they don't show for redownloading, as described on the page that you posted from. If they are being synced back to your iPad then you must still have them on your computer's iTunes library - you can select them in the Apps part of your computer's iTunes library and delete them from there (and delete them from your iPad so that they aren't copied back to your computer when you next sync), that will stop being synced back to your iPad.