Here's the thing; based upon the numbers that were posted after the price drop, it looks like the PS3 saw nominal benefits in terms of total number of hardware units moved.
In other words, it looks like dropping $50 of potential profit per unit didn't result in shifting a significantly larger number of units.
But, consider what type of numbers the PS3 would have posted had the entry price remained $299. I believe the decision was less about being able to claim they sold more units than the Xbox and more about cutting off drastic drops in sales YoY that may well have happened at the higher price point.
As for whether they should have, on one hand you could have an extra $50 per unit of profit, but while selling XXX fewer numbers, giving the impression that the platform has run out of momentum. On the other, you surrender those profits, but maintain higher sales keeping the momentum going.
Ideally, any significant price drop would have been accompanied by a visible redesign giving the updated model a marketing point for repeat sales from previous customers while simultaneously opening up the product to lower price point conscious consumers.
I'm assuming the price drop was accompanied by internal hardware changes resulting in slightly cheaper per unit production costs, but doubtful they were enough to offset a $50 drop in retail price.
There is a point at which a complete overhaul design is necessary to significantly reset the bar for lower per unit production costs and I think the current PS3 model has hit that point.