If you get the corded HF stuff it actually does last a while. I still have my 4.5" angle grinder from over 6 years ago, and I seriously abuse the snot out of it. I have yet to change the brushes (and you always get a spare set) probably due to losing them.
The battery powered stuff is where it gets hit and miss. Chargers fail often, and battery packs tend to lose capacity even when properly maintained in accordance with known practices (NiCd, Li-ion respectively).