Think about it this way, if planes were to attack infantry they'd end up dropping bombs and rockets on a single infantry unit, they can't distinguish between a single unit or a crowd of them, so a plane would end up wasting its heavy ordanance on single units instead of for targets that actually need them.
It is possible for planes to engage using their guns on infantry for strafing runs, I've seen AI do it, but still that leaves them defenseless against other air targets they might encounter and they'll always take priority in the AI's routines. To qoute Saving Private Ryan "..the airforce isn't gonna spend ordanance on one machine gun..."
In my opinion its not an issue at all, if you're playing single player and you've made yourself a mission with planes available, just make it playable, switch to the plane and bomb whatever you like. If it's multiplayer, try and persuede your pilot buddy to do a bombing run on infantry (they'll probably tell you its a waste though).
If its that vitally important to you, script it yourself and incorporate it into the missions you make. As a feature for I44 though, its not something we'll be doing as its innacurate with regards to realism, and something that would waste a valuable asset on something you can just as easily shoot yourself.