I would hesitate to rely on chimp's example of stalled technological development, when applied to another hypothetical planet where a primitive tool user species is NOT competing with more advanced users. Basic ecological theory holds that different species never occupy the identical ecological niche. If chimps stopped being semi-arboreal, which they would have to if they're going to do much in the way of hauling tools, then they'd be in more direct competition with forest-dwelling hominids. I understand hominids evolved to utilize grassland areas as well, but they also utilized forest resources. My guess is that hominids beat chimps to the punch of extensive tool-using, and will deny chimps that niche as long as the hominids stay around. On the hypothetical planet discussed above, the first primitive tool user is not blocked in development.

Anyway, let's say I'm wrong- what does a mere 5 million years prove? Even the pessimists believe Earth has another 500 million years before the oceans boil away. Give our chimp friends, and their counterparts on other planets, the time they actually have available to them, and they might learn a few things.