They didn't sell Office to 8 million Mac users... from my experience, they may have had a 25% market penetration on Mac and many of those were using the previous version of Office. Remember, Apple was including a copy of ClarisWorks with every Performa Mac they sold.
Their crappy browser was most often replaced with Netscape as soon as the new buyers could switch... all you had to do was run Netscape once and it asked if you wanted to make it your default browser. Most did. IE was considered a joke by most Mac users. As soon as the 5 year agreement expired, Microsoft dropped support for IE on Mac... and Apple replaced it with Safari.
Microsoft had to pay a yearly license for the software patents that Apple owned. Apple got to use the Microsoft patents in perpetuity for nothing.
There was no 10 - 1 profit on the deal... The stock sale was a way for MS to have a way to recover its initial payment to Apple... that's why it was called a negotiation... an exchange of plusses for both sides... but Apple got the lion's share of plusses.
According to MS at the time the settlement occurred they had 8 million Office for Mac users:
http://www.news.com/MS-to-invest-150-million-in-Apple/2100-1001_3-202143.html
“More than 8 million customers use Microsoft Office for the Macintosh, making it “the single largest revenue Mac application,” Maffei said.”
Lots of people never bothered to replace the default browser, that’s a large part of why MS won the browser war. Most users aren’t savvy enough for that, or just don’t care, they use what’s on the computer and learn to be happy with it.
Sorry but you admitted they sold the stock at a profit, add the revenue from Office and you’re talking a minimum ROI of 10X. Not something that any sane person would consider being taken to the cleaners.