Ageless qustion !

[MasterFlex]

This is more phylosophy than anytning else, unless someone has a sure answer.

Punches do no resemble pushups. Former are unilateral, accelerated by the legs and midsection.

How come people use pushups in every combat sport. Is that for general conditioning. I can't tell you how many times instructors said "pushups will improve the power of your punches" Most say it, just to say it.

[koltz]

cause pushups resemble the motion ( extending the arm foreward ) nuff said.
you won't punch for shit without extending your arm foreward to deliver the force. but you could deliver a deadly punch for a stiff legged position with relexed abs and no twist just with enough pressing strength ,

[Drunken Panda]

Also, pushups will improve your general strength, be it maximal strength / raw power (from doing one-hand pushups, handstand pushups etc.) or strength endurance (high reps) etc.

While there is a great deal of skill in throwing a punch (it never ceases to amaze me how many people when the first start training at Kung Fu simply don't have a clue how to throw an effective punch), it requires strength behind it to be effective and strength endurance to throw multiple effective punches (or other strikes) without tiring.

Strength is useless without skill and speed.
Skill is useless without speed and strength.
Speed is useless without strength and skill.

All aspects must be honed if one is to be effective. Being the strongest person alive wont help if your too slow to throw a punch / not skilled enough to get it past an opponents defences. Being a really fast puncher is no good if the punches have poor technique or if when they land there is no strength behind them. And having a really good punching technique is no good unless your fast enough to land it and cause some harm when you do.

Sorry, I went off on a tangent there. Anyway, I hope this philosophising was helpful, or at least thought-provoking.