I'm going to answer your previous question, about Help vs Rigby, here.
You're absolutely correct, the Beatles made pop music in their later career, too. In my opinion, the Beatles were throughout their entire career a pop band before anything else. They were a rock band too, sure, and they had elements of folk, psychedelia, and avant-garde in their songs...But they were always a pop band. From I Want to Hold Your Hand to Come Together, they always did pop. The difference, though, is that they got a lot more innovative with their pop sensibilities later on.
Look at Help!...Despite being a good rocker and an all-around good song, it was also a pretty safe and conventional song. It's something you can get on your feet and dance to, which is what pop up to that point (and mostly since, too) was all about. The lyrics are desperate and a little bit deep, if not exactly Hemingway, but this wasn't really anything new in that era.
Now, Eleanor Rigby is a different beast altogether (and I should note here, I do like Help! more). It's a mellow song, and it can be called a pop song. However, no one's going to dance to it. It's more the type of music you listen to on a rainy day on a bus staring out the window. And it's a lot more innovative. The strings are an important part of all that. Plus, there's a lot of stuff going on in the background. There's nothing particularly safe about the song, nothing that guarantees a mass audience other than the name "Beatles" on it. The lyrics are very sad, and also abstract and imbibed with a lot more poetry. There's a canvass of an entire city in 2 minutes. They really broke new ground here. That's why I'd say that it's less poppy than Help!
Of course, if we just take pop to mean "Not a rock song," then that's a different case entirely.