UPDATE Aug 27 2013: It is now almost 3 years since we looked at this analysis. Since then Amazon and Google have most definitely shown that they are platform ecosystems (hardware, software, content and goods) that will compete for the hearts and minds of businesses and consumers alike. Even Facebook who entered the public sphere in the last 2 years is giving Amazon a good run for their money. This is the power of having millions of eyeballs look at your content daily. It is akin to a new massively powerful media company. While these companies are in decidedly different yet overlapping businesses, these 5 companies, in my mind, will form the different models of technology adoption and innovation for the rest of this decade. The real question is what course Microsoft will take? Will they indeed be the "IBM of the 21st century" maintaining the legacy of the late 20th century for the better part of the beginning of the 21st century?
AAPL Market Cap data by YCharts
UPDATE Oct 6 2011: It is now almost 1 year since I wrote this article and Apple continues to have a larger market cap than Microsoft. Steve Jobs passing kind of underlines the eternal competition between these 2 tech giants. The chart looks very similar.

The chart above shows a historical return on investment (ROI) between Microsoft (MSFT) and Apple (AAPL) going back to the early 80s when both companies become public corporations. Recent returns over the past 5 years put AAPL slightly above MSFT in terms of market capitalization and way above Microsoft and Google in ROI (see chart below). But the returns over a much longer period are startingly different.
While Apple was struggling in the mid to late 90s and working to get its mojo back with the return of Jobs, Microsoft was absolutely crushing it, gaining market share every year in both the home and the workplace. After shipping Windows 95, lauded to be the most compatible and available operating system "for the rest of us," Microsoft went on a tear to solidify their lead by cementing a stable OS with Windows 2000 and essentially locking in 90% of desktops to Windows XP. Go around most enterprise offices and you'll see Windows XP still running on most desktops. Vista and Windows 7 are a long ways from being adopted anywhere other than by consumers who buy new laptops and desktops for their home use.
And with those millions of software licenses Microsoft was able to create huge shareholder value -- mostly from their enterprise domination. And then the cash was used to buy a variety of products that we know of today mostly as "bloatware." There's a ton of useful stuff that is used by many, but when is the last time you saw a Web 2.0, high end, high volume business running on .Net as an infrastructure? I compel you to find any large Website using .Net as a platform.
So what has been happening the last 5 years or so?