Market share vs. installed base: which is more important?

One of the reasons I don't get that excited about numbers from market research groups is due to the fact that so much of the data collection methodology and the slivers of detail that can make or refute a single number are never publicly mentioned anywhere. This includes NPD, Forrester, IDC and other well-respected research groups.

But, as an investor, I want to know extreme detail about everything -- as to make the best and most informed decision. This article over at Roughly Drafted gives a pretty concise but detailed example between two market scenarios that are sometimes compared but should not be: the PC vs. Mac fight from the late 80s and into the 90s and the iPod vs. Zune fight going on right now between the same two companies -- Apple Inc. (NASDAQ:AAPL) and Microsoft Corp. (NASDAQ:MSFT).

The vivid picture painted here is that numbers and very true (but not all-inclusive) statistics can allow either company (or any company in any industry) to cherry-pick market share and installed base numbers to the benefit of product marketing, but which may only explain a sliver of the overall strategy and success or possible failure of a product (or an entire industry section of products).