It's hard to avoid simple rules when first teaching/learning anything which requires a great deal of skill. Poker is like many other things, in that there are basic guidelines which are generally true, and need to be learned, but that have exceptions that can only be learned with experience. I think that the basic guidelines are a good thing, and when teaching a beginner, one should mention that there are exceptions that will be learned later. Teaching all the exceptions right away is just putting too much information on the table at once which can't effectively be used. A few examples from other games ...

In bridge, there are many guidelines that beginners are taught which are usually true but have many exceptions for expert play, such as

Cover an honor with an honor,
When in doubt draw trumps,
Always lead partner's suit.

In chess, one is taught to develop one's pieces as quickly as possible and control the center, but more advanced players learn when plays that take the initiative are superior to developing plays. Among many other exceptions to well known rules are that doubled pawns are not always weak, and rooks do not always belong on the open file.

I think it is wrong to teach simple rules as gospel truth. But I also think it is counter-productive to try to teach the beginner everything at once.