For aircraft, weasels (aircraft made to shoot ground to air defenses) and interceptors exist solely to give bombers the best chance to deliver their payload safely. In one form or another, all avenues of the airforce exist to either protect its own bombers or to shoot down enemy bombers except transports.
I think this is a very oversimplified view of air combat. For one thing, the term "Bomber" is quite nebulous in today's aircraft world. The F-15 is technically considered a Fighter Jet, but it can carry quite an explosive payload lethal to ground targets as well. The Stealth Fighter can carry a nuclear missile on-board and be immune to most radar detection.
Even the pure Fighter roles can be dangerous to ground targets. In other words, Anti-Aircraft Jets do not exist just for the sake of destroying enemy bombers. That is one of their roles yes, but not all of them. Controlling the airspace above a battleground is extremely important for survey and reconnaissance information. As they say, knowing is half the battle. Fighters keep the air clear so that the recon aircraft and drones can gather information about hostile threats and future targets. This is just as, or more important than the role of protecting Bombers, because Bombers won't know which target to strike if they don't have any intel.
Also, all military aircraft used today are multi-million dollar machines. I hesitate to say that any of it is designed as cannon-fodder.
For ground combat, infantry and mounted infantry is used to suppress and screen for the heavier and more powerful armor, for while the armor is in many ways stronger they are blind. This is a very murky situation, but it is common enough in offense and in defense to bring up.
Infantry can sometimes be used for reconnaissance for a tank yes, but this can be done with binoculars and high-tech gadgetry, not by having to be on top of the enemy. Tanks are actually designed to soak up fire for the infantry in order to give them cover, they are not a back-line weapons like artillery. In other words, I don't see how the introduction of the Tank to the battlefield suddenly makes infantry into cannon fodder.
I really have no idea, just curious: when's the last time a naval combat action got to the stage of two battlegroups getting into shipboard cannon (not guided-missile) range of each other?
Well the last Battleship was decommissioned what like, 20 years ago? If that tells you anything.
I can't speak for how naval combat worked in the olden days, though I would assume that protecting the Aircraft Carrier at all costs was the priority.