One of the minor "features" Microsoft included in the Internet Explorer 10 Platform Preview released earlier this week was reduced operating system support; it will only install on Windows 7, leaving Windows XP and Windows Vista users out in the cold. Microsoft confirmed to Computerworld that this was no accident, with a spokesperson saying "Windows Vista customers have a great browsing experience with IE9, but in building IE10 we are focused on continuing to drive the kind of innovation that only happens when you take advantage of the ongoing improvements in modern operating systems and modern hardware."

That's a claim that's hard to make any sense of.

When the company announced that Internet Explorer 9 wouldn't support Windows XP, the decision made sense. Though it meant cutting off a large number of Windows users, Internet Explorer 9 was written to depend heavily on Direct2D and DirectWrite for all its hardware accelerated high-performance graphics, and on Windows' Mandatory Integrity Control (among other things) for security. Direct2D and DirectWrite were both introduced on Windows 7 and back ported to Windows Vista; MIC was introduced with Windows Vista. In neither case were the features available on Windows XP, nor even readily ported to that operating system.

But no such disparity exists between Windows Vista and Windows 7. Windows 7 is undoubtedly better than Windows Vista. It's three years newer, improvement was inevitable. What it isn't, however, is substantially different. Windows Vista did the hard work—radically new display subsystem, new audio subsystem, new media framework, and so on. Windows 7 just consolidated those changes. As we noted when we reviewed Windows 7, the decision to upgrade from Windows Vista was not entirely clear-cut.

So unless Microsoft is planning to back port some big chunk of Windows 8 functionality to Windows 7—and then make Internet Explorer 10 depend heavily on that functionality, just as Internet Explorer 9 depends on Direct2D and DirectWrite—the talk of "ongoing improvements" is hard to fathom. Windows 7 is an incremental improvement on Windows Vista now, and it will be that same incremental improvement this time next year. To imply that Windows 7 is somehow "modern" in a way that Windows Vista is not is disingenuous in the extreme.

There's also a question of support. Windows Vista is still in mainstream support. This means that it's still, in theory at least, eligible for nonsecurity bug-fixes and improvements. It'll be in mainstream support until April 10th 2012. Assuming Internet Explorer 10 comes about a year from now—just as Internet Explorer 9 took about a year from its first Platform Preview at MIX10 to the final release—then, depending on which day of the week the software ships, Windows Vista will either still be in mainstream support when Internet Explorer 10 ships, or will have dropped out of mainstream support by a matter of days, after having been generally available for just over five years.

In contrast, when Windows XP received Internet Explorer 8 on March 29, 2009, it had been on the market for more than seven years, and it too was just on the cusp of losing mainstream support (Windows XP Service Pack 3's mainstream support ended on April 14, 2009).

Of course, Windows XP had one thing that Windows Vista doesn't: substantial market share. Windows Vista's usage is declining, and by next April it will probably be down to five or six percent of the market. A small share, to be sure, but still many tens of millions of users. Users that will be ceded to the competition. Microsoft may feel that such a small market share isn't worth supporting, but if so, surely the company should say so instead of fobbing people off with comments about "modern operating systems".

Whatever the real reason, this is a pretty raw deal for Windows Vista users. Not as bad as the Ultimate Extras farce, but bad all the same. It also means that when Microsoft released Internet Explorer 10, it is likely that it will support just one operating system, with a second, Windows 8, due later in 2012. The company is already being criticized for supporting a mere two operating systems with Internet Explorer 9. Cutting back to one, leaving Windows Vista users out in the cold, is hard to defend.