The way I think of it is like this:
Consoles are like an extremely heavy weight. Games are like weight lifters. If a console's weight, which we'll say is determined by price, accessibility, marketability and weight has 1000 weak weight lifters (games) it can do well. Otherwise it needs 100 normal weight lifters, or 10 professional weight lifters. 'Big games' are more like professional athlete like weight lifters. Since they get so much more attention, the multitude of small games go to other platforms.
So if we say PS3 'weighs' 500LB then it needs 50 games that can lift 10lb to be lifted from the ground, or it needs five games that can lift 100 lbs. If we attribute games that lift 100 pounds to 5+ million sellers, PS3 is still 'too heavy' to get a big game boost from the addition of someone who can temporarily carry some of the bulk. PS3 has maybe three eventual five million sellers right now - Motorstorm/GTAIV/COD4. They carry like half the load...but the rest of the content isn't as 'strong' in lifting the weight of PS3. I think PS3 is about a price cut and two big games short yet of seeing a long lasting boost from a big exclusive simply because of how much content it shares and how difficult that makes it to 'lift' the platform weight.
Once a console has a small number of big games or a multitiude of small games working at once it is easier to get boosts, even if the price doesn't drop that fast.
In terms of weight, Wii is at like 250 LB, but has nine 5 million sellers (Wii Fit/Mario Kart/Brawl/Wii Sports/Wii Play/Galaxy/Zelda/Mario Party/Mario & Sonic) which is why its essentially been 'lifted' so high for so long.
People are difficult to govern because they have too much knowledge.
When there are more laws, there are more criminals.
- Lao Tzu