They sound the same alright, and I think ALW is a dillweed but I also don't think it's impossible that two separate musicians could come up with a riff that's nothing but going up and down 5 semitones. It's like getting mad at someone else's kid who also decided to stick two red duplo blocks together.
There's a Procol Harum song called Conquistador from 1967 that uses a similar descending riff around the chorus. I always thought Pink Floyd took it from that (possibly subconsciously) since the two bands toured together.
