I also find it odd, that people in American TV series wear shoes at home. I am from Germany. In Germany we either wear slippers, socks or walk barefoot at home. When we have guests, we often offer slippers. Sometimes we allow guests to keep their shoes on. But it is more customary to take one's shoes off, when you visit someone else. I watched an interesting youtube video by an American woman who lives in Germany. It was about things, you shouldn't do, when in Germany. One of them was wearing shoes inside. She suggested to bend over and pretend to take off your shoes. If the host is ok, with you wearing shoes in the house, he/she will immediately stop you and tell you that it is fine. If the host says nothing, then you just continue taking off the shoes. That was spot on. 

That was the video:

https://www.youtube.com/watch?v=vjnhm1QeGyU

Hey! I've been wondering the same thing... I am from Finland and I can say that we never wear shoes inside. We don't wear slippers either, we just hang around with socks on, or even barefoot! It's the same in other Nordic countries as well (Sweden, Denmark, Iceland and Norway). 

I find it weird that some people wear their shoes inside... I could never do that! xD

Some do, some don't. You can't generalise about 'Westerners'.

Different countries have different customs, and there are many variations within countries, too.

I really liked Miriam' s description of the 'How to..' video. I hadn't thought of it before, but that's exactly what happens. When someone comes into another person's house, especially if the hallway  is carpeted, there's generally a moment of hesitancy. The visitor often looks down at the carpet, makes a slight downward gesture towards their shoes while looking enquiringly at the host, perhaps with an offer of 'Should I ... um..?'.  At this point, the host either says 'No, don't worry about it' or (slightly apologetically), 'Er, yes. If you don't mind..'   Spot on, as Miriam said.