The article goes into the premise behind Microsoft's decision. It isn't their desire to shut out XP users. The Windows 7 installer still supports automatic dual-boot installations, which would allow someone with an existing XP install to have 7 sit side-by-side while they transition. Forget about keeping your library of installed applications, however, as those will all have to be installed fresh. This differs from the launch of XP, where Windows 98 and Windows 2000 users both enjoyed the ability to do upgrade installs.
As time goes on, and people get machines pre-installed with Windows 7, the problem will become less important. Still, there's room for criticism here – Microsoft has a lot of PR to make up for due to the perceived disadvantages Vista had and the dismal initial launch. Though Redmond has addressed most of the criticism, they still have a lot of unhappy customers, and as the article brings out they should seek to reach out to as many people as possible. It does seem in this instance that Microsoft is neglecting a huge pool of users. What's your take – is Microsoft making a mistake in not allowing upgrades from XP?