We all knew that the 1990s tech boom would change the world. But then a funny thing happened: For years brick-and-mortar companies happily coexisted with their e-rivals. Borders, for instance, actually increased sales from 2000 to 2005 as it dueled Amazon (AMZN). Now those days seem to be ending. Digital companies are so big, and growing so fast, that they’re obliterating old businesses. Consider these four examples: The U.S. Postal Service says it will be insolvent by the end of 2011 without a bailout. Blockbuster and Borders have filed for bankruptcy. And music stores keep closing. Texts vs. Mail The U.S. Postal Service is on track to lose $6 billion this year, as e-mails and texting reduce mail volumes faster than postage fees can rise.