Do regular tvs with pip have lower resolution than those without
 

Like the title says...I have two 27 inch Sanyo tvs. One has pip (picture in picture) and the other doesn't. It looks like the tv without the pip has a slightly sharper picture than the other with pip.

Is it all in my head or is it real?

It may be real but it isn't necessarily related to PIP. Lots of things contribute to picture sharpness including the apes who delivered it, the tube type, age, etc. Even tubes next to each other on the assembly line can vary to some degree.

Magnetic fields (including tube position relative to the Earth) and anything that draws power can mess with the image. If completely bored try setting them next to each other (facing the same direction) a foot or more apart and away from walls and powered devices/speakers. Degauss if they allow it, and compare.

Never really noticed till you brought it up, but i'll check it out next time I head to my parents home, thay have a few tv's with pip and without.

There are a lot of video circuits in a TV. How well they are set up (alignment)
in the factory will make a great difference in the final picture. (Maybe less than in the "old" days.) Bandwidth and flatness of responce and phase relationships in the video signal path are very important.

The user also contributes to making the picture better or worse.
I don't know how it is in the USA anymore, but in the 40s-70s NTSC
also meant Never The Same Color.

also if your cable line has a splitter anywhere in it than that could degrade picture quality.