I have seen trailers with both carpet and plastic/composite bump stops. I would agree that the caps are probably there to prevent the carpet from ripping
I didn't know they made caps for the carpet, I figured it's an expendable item and easy to replace. I bought a 6'x8' roll of black indoor/outdoor at Lowes for around $20, enough to re-cover the front stops many many times.
Soo.. if you want to keep the plastic caps looking nice do you cover them with carpet? Chicken-Egg situation.