B.M.
well, it's normal in that I would say a ton of kids do it and I don't think it warrants a dr visit.
However - realize that picky eating in MOST (not all) cases is 'learned' behavior. I'm not knockin' ya - we all have fallen victim to our kids 'demands'. You say he 'used ot eat a lot more variety, but now he has stopped'. I would venture to say he has stopped because he's a smart little guy and has figured out how to get what he wants.
If you want this behavior to change, though, you need to change how you relate to him and what rewards and consequences there are about how he eats (natural rewards and consequences - I do not believe in punishment or actual 'rewards' around food).
Additionally, I totally believe that food does not have to be 'traditional' to be acceptable. So, I think a banana for dinner is fine. You always want to look at toddler nutrition on a several-day-in-a-row rolling snapshot. so, he may eat very little one day, but a lot the next. Toddlers do a MUCH better job listening to their own bodies than we do, so it's not something to stress out over (easier said than done).
However - I personally (and I guess you didn't really ask this) wouldn't get in the habit of making him special food - or coddling him like letting him sit in your lap to eat. In order to teach him proper nutrition he needs to sit in his own seat, eat what you prepare that is nutritionally beneficial to him (and part of that is expanding his taste buds) and start learning how to use his own fork/spoon etc when the time is right. He also needs to learn that you are the parent and you set the ground rules.
One thing I do know - toddlers won't starve themselves to the point that they will do damage to themselves. They WILL starve themselves to the point they have learned that mommy will give 'em the good stuff. So, if you give in he is learning how to get what he wants (a skill that he will perfect by about 4) - so the more consistent you are now the easier it will be for you later.
The food stuff is tough - good luck!