RacerX said:But at the same time they also learn the lesson of using their position to force upgrades. While they may have been keep backwards compatibility alive in their application environment, within their applications they have been making their formats less and less backwards compatible.
The Office case you mention is a good counter-point to what I mentioned above. In the office business software suite market, Microsoft are so utterly dominant, they can afford to forego backward compatibility; in this case to force previous versions of Office to upgrade.
Which, when you think about it, only becomes necessary if the new version isn't providing sufficient innovative features.