No, that is the point on building your spec to get ready for the endgame. Most games dont even last to level 20 anyways.

I figured that was the idea - you "skill" your Demigod to your playstyle, and do not buy skills which you don't find helpful.

If the level cap was such that you could take everything, there would be little strategy in deciding what to take when you level, as you know you'll be able to get it later.

this is a thing called choices. you choose between Depth (maxing out just a couple of specific skills) or Breadth (taking lesser points in a greater number of skills). its a trade off. it makes things more interesting.