Why 4096-bit RSA certs when you can have ECC certs?
There's also folks who don't entirely trust ECC because it's "too new". To be fair, RSA isn't broken, and 4k is sufficiently big to be safe even with a partial break.
Isn't RSA much more computationally expensive than ECC? What hardware can do RSA but not ECC?
/me sits down to be schooled
EDIT: Unless you're referring to embedded systems that can't be updated?
Actually, not just embedded systems. There's HSMs (hardware security modules) which also can't be updated to support new functions. Often this is because the underlying primitives have been implemented in fixed-function hardware to prevent timing, power and even RF analysis.
(I know we're not there yet :P)