I've heard that too...but I'm not sure I believe it. Also, you have to think about the "square footage per toy" you have in your home. The bigger it is, the more toys they should probably have
That way, you can have a few in each room that get rotated through the house-we have some in the bedroom, some in the playpen, some in the hall, the office, the living room, the family room, and outside! When I go to pick them all up, there are LOTS, but that's ok. They carry their favorites around more often than the others.
I put their toys out in thirds-meaning I let them have about a third of their toys, and then in 1-2 weeks I put those away, and bring out others. When toys get too "loved" I either mend them or toss them out and replace them with new. They don't get too bored this way.