I'm actually glad that Beth have canned it seeing as it was never done very well anyway...
Besides, if Beth has decided that it is canon in Skyrim that spells can only be purchased (for some reason) then that's that.
In a reality of suspended disbelief, spell making would probably be an incredibly difficult, problem filled and dangerous past time that only the very best of wizards could manage and even then with less than satisfactory results.
Just my opinion. Thoughts?