Yeah though battleships and bombers aren't as handy as APCs in some circumstances, and aircraft carriers are horrendous in traffic.
If you're referring to the M1 tank I think it's being retired because they're old enough now that the maintenance to keep them running is high enough that it's cheaper longterm to mothball them, sell some off, and spend money on new tech. They kinda did the same thing with the SR-71 Blackbird years ago. The maintenance cost just to keep them flyable was prohibitive, so they started using sattelites for the same sort of thing.
It may also be because a traditional mechanized land army is relatively difficult to deploy compared to infantry, wheeled vehicles etc, and less useful in urban environments. I suspect advances in surveillance, sattelite imaging and communications, as well as experiences fighting insurgents rather than regular troops have made a flexible, fluid, high tech army more important than a slower, more heavily armored vanguard.
