I think it has to do with neither pride nor discipline. It's all about business.
Microsoft won't make much money by breaking backwards compatibility; in fact, they'd lose billions if they did. Think of the hundreds of millions (if not billions) of business licenses they have sold. Business customers want their old apps to keep working. Yes, I'm talking about the same people who still use IE6. Whether you like them or not, these are the customers who purchase thousands of licenses each, and there are lots of them. Losing these customers could hurt Microsoft just as much as, if not much more than, losing tablet-toting consumers.
Of course, Microsoft doesn't want to lose either market, so they'll produce a version of Windows that has both complete backwards compatibility with existing Windows apps, and a fancy shell to appeal to tablet users.
Microsoft won't make much money by breaking backwards compatibility; in fact, they'd lose billions if they did. Think of the hundreds of millions (if not billions) of business licenses they have sold. Business customers want their old apps to keep working. Yes, I'm talking about the same people who still use IE6. Whether you like them or not, these are the customers who purchase thousands of licenses each, and there are lots of them. Losing these customers could hurt Microsoft just as much as, if not much more than, losing tablet-toting consumers.
Of course, Microsoft doesn't want to lose either market, so they'll produce a version of Windows that has both complete backwards compatibility with existing Windows apps, and a fancy shell to appeal to tablet users.