My experience is that television is addictive. That's why so many children will sit and watch tv all day if allowed to. My daughter is no exception. If I let her, she will watch television all day every day. She loves to read, to play outside, ride her bike, do arts and crafts, play games, but she will choose television over everything consistently if I let her, and she's proved it over and over again. And note - she was not like that when she was a young child. This developed over time.
I think that your son watching tv and liking it is fine. I would suggest you begin to teach him early that he watches say an hour of television on any day, even now when he may not understand how long an hour (or maybe half hour at his age) is. You could say, "Oh, do you want to watch your half hour of tv now?" when you go to turn on the tv.
I make this suggestion because that is what I have to get through to my daughter, and she understand the rule, but it would work better if the rule was a part of her entire television experience. She is 10, and she doesn't get to watch tv every day, because she has a busy school day. She is allowed an hour a day though (of computer or tv time). I notice that when she doesn't have access to the tv (first thing to go when she is on punishment) she reads even more - and she does read a lot.
I also found that she was watching a lot of tv if she was staying with my family members. So to balance that out, she pretty much never watched tv at home. This all went to the pot when I moved in with my mom. Then her love for television was fed by my mother's tv addiction, which honestly has also affected me. I'm actually getting rid of all televisions when we move.
As children get older, it gets more difficult, the entire tv thing. There are a million shows on the cable and network stations, and children don't mind watching the same rerun of a show a dozen times. They have so many shows for every age group, and they will want to watch all of them. And they'll seem fine, but there are so many stereo types, including gender based stereotypes in all these shows, that tell your little boy just who to be to become a perfect consumer as an adolescent, teen and adult male.
I am susceptable to tv the way children are. I've actually noticed that I've begun to spend the week looking forward to Sunday and Monday when The 4400 and Kyle XY come on. I've never been like that, but these shows are designed to suck you in, and children are less able to see it or control their reaction to it. The marketing campaign just around a new episode of a show is ridiculous. Children will know a week in advance when a new episode of That's so Raven or The Suite Life of Zack and Cody will be airing.
I imagine you know someone who builds their life around their shows - when you can call them, when they have to be home - or who just sit with their remote and watch tv all day. I find that our minds are very susceptable to it.
I think the best thing I did was get rid of the televisions before my daugther turned a year. Then we never could turn to it. She was used to no tv's at home, and though she got to watch tv at other's homes, didn't expect it at home. I know a lot of people wouldn't be prepared to do that, but she definitely was better off without it, which is why we're going back.
Eventually my grandparents' bought her a tv, but we seldom watched it. She actually came to me once and said, I don't know what to do if I can't watch TV right now. There was nothing appropriate for her to watch on our non-cable tv set at that hour. She never had that problem when there was no tv, she always has every activity under the sun! When I mentioned that I could get rid of the TV if it was making it hard for her to think, she suddenly came up with all kinds of ideas, and entertained herself without the television.
Anyway, Sesame Street is a great show, and I think nothing is wrong with watching a little TV, I'm just pointing out some of what I've observed and experienced so you can consider those things as you plan and develop a culture in your house around the use of television by the members of your family.