bramley - 5:59 am on Apr 7, 2011 (gmt 0)
At some point in the past the decision may have been how well does this page match the serach term; now it is how well, but diluted by how well it matches other search terms.
That's why long-tail results are seen as holding up better - because that it the best match of that page. And if there is a more genral page, it is too weak to rank (perhaps just a menu or ble widget, red widget etc).
In other words page match is not additive but apportioned (jack of all trades, master of none).