It's not unheard of no, but if you have to rule out two for some reason it's because of some other arbitrary choice. In the first instance (haven't yet looked at the second and third one) it has to do with the fact that a sum of "two" was chosen arbitrary. You can come up with other things that requires you to exclude primes up to five.

[–] kogasa@programming.dev 1 points 1 year ago

Okay? Like I said, it's usually to rule out cases where 2 is a trivial edge case. It's common enough that "for any odd prime / let p be an odd prime" is a normal expression. That's all.