The "no risk / no reward" argument really doesn't pan out very well when it comes to scoring perks...
If it did, it would stand to reason that you'd get more perks for kills in a perk plane, than in a plane that's "free". After all, you're risking a bunch of perks (in addition to your time) if you attack a bomber in a 262, but you're risking only your time if you attack a bomber in a Spit1.
Perks seem to be a reward for "skill", or at least success, and are more closely tied to "difficulty" than to risk. If you fly a tougher plane, you get more perks. Likewise for beating an easier plane, or for making kills for the team with fewer numbers.
Also, perks can only be used to "purchase" similar vehicles. Fighter perks are scored in fighters, and are used to "purchase" fighters. Perks for guns would be pointless, since there are no guns for "sale".