There certainly is! PT_INTERP isn't mandatory: if it's not set, the executable has no interpreter, thus cannot use shared libraries and must be self-contained.
(Also, if pure statically-linked binaries cannot exist, what do you think /lib/ld-linux.so.2 is? If ELF interpreters don't count because they are technically shared objects and relocate themselves, /sbin/sln surely does. No relocation, no PT_INTERP: static as static comes, and on pretty much every system.)