Excel was actually always an in-house Microsoft thing. Originally it was called Multiplan and was actually very popular for a while. Like the poster mentioning Word, it's a contemporary of its main competition, not a copy.
IE was originally a licensed and rebranded version of one of the old mosaic browsers. I'm sure the name is on the wiki somewhere, but it was definitely not attempting to clone what would be the Gecko engine.
The fact is, Microsoft has always tried to compete, not copy. They've tried to do things better than the competition and not exactly like it. Like any company, they've had their share of failures and successes, but it's DEFINITELY not fair to say Microsoft has been riding the coattails of anybody - especially not in the modern day where its success was mostly through buyouts of very successful, good pieces of software. Every large company does this.
None of this, however, hides the fact that the Metro interface is awful for desktops and trying to force it on the desktop in order to force users to use their app store is and already has sewn some seeds of contempt. Microsoft is definitely making a HUGE gamble on this and arguably a mistake as well.