I definately have thought about momentum. You're just thinking in a rather limited context when you read my statement of "50% more sales".
Momentum is just another factor that affects sales. One way of putting it is whether a $50 price cut tomorrow will result in enough of a sales boost by years end compared to a price cut in August. After holiday 2008 momentum will have evened out. If the difference in Jan-Dec sales between the scenarios is about 50% more than the Jan-July sales of the first scenario, then it's probably worth it. For example:
1 - $80 cut in August:
Jan-July sales of 4M, Aug-Dec sales of 8M.
2 - $50 now, $30 more in August :
Jan-July sales of 6M, Aug-Dec sales of 9M.
Scenario 2 costs MS $300M more in loss leading, but by years end they get 3M more consoles out. 3M is 50% of 6M, so it looks like this outcome is favourable (note how this means MS needs to get back $100 per console in games/accessories/downloads to match the profit of scenario 1, which is reasonable). Of course, my numbers are pulled out of my ass. It's rather optimistic to think making a price cut now would have such a big difference.
IMO real momentum isn't really generated by price anyway, and it's the games that do that. Look at the PS3 sales spikes after price cuts that withered away in a few weeks. What's really going to get the PS3 going is GT5, and I don't think a cheaper 360 is much of a lure away from that.
But the thing is, it's impossible to predict the impact a pricedrop will have and when. Especially longterm. As one pricedrop sets the stage for an earlier drop next time etc etc
All you can do, is look at your competition, try and predict what they will do, and then do whatever you think you have to to increase your momentum.
Who knows what impact a $100 pricedrop in April, before GTA would have?? Hard to say really.
So, I think the console makers generally have to choose a strategy, and how aggressively you decide to drop price is part of that overall strategy, and you don't get hung up on short term 3 month sales figures.
Who's to say if MS's reactive pricedrop strategy is a good one, I don't know. But I do know how succesful Sony's strategy was with PS2, and while you may point out that they would have been succesful regardless (true), I would argue that the mere fact Sony felt they needed to do so, with all their experience and wisdom, shows that there is more to the equation that the simple formula of short term install base:revenues lost.
For example The position they created with PS2 put them in place to walk away with profits this generation, they screwed it up, but how much is that
potential worth?
Sometimes, a runaway success like the Wii would obviously change your strategy. And I think, with MS, the initial lack of success for PS3 has changed theirs, but the time is now(2008) to be aggressive, and to push that cost advantage, or they could easily see their lead slip away.
Which impacts their profits all the way down the line, for years and years on the current 360, and it puts Sony in a stronger position
for PS4. How much are all those lost revenues worth?