Singleplayer RPGs and MMOs are absolutely different. They are anything BUT similar.
Let me give You an example.
Hewlett Packard makes printers. Acer doesnt make printers.
So when Acer makes their first printer, it will be bad.
When Hewlett Packard makes another printer, it will be much much better than Acers, cause HP has a lot of experiences in making printers.
Both companies work in IT, but printers and PCs are different.
Just fyi, HP = ArenaNet, Acer = Bioware in this story.