Apple as we know it also stole some of its founding ideas from Xerox. Xerox even sued Apple for that while they were busy suing Microsoft for stealing something they stole from Xerox. Ironic.

Video 1: Steve Jobs describes sweetly how he stole from Xerox

Video 2: A demo of Xerox Interface that was demoed to Apple team

Video 3: Steve Jobs about Microsoft stealing their Ideas

Finally its neither Apple nor Microsoft that lost the opportunity but its Xerox who could never make a dime in the PC industry.