Microsoft's response to Apple's software update pricing ($29 for Snow Leopard) is interesting: $30, but only to students.
Businesses, families, and others won't be eligible for the discount. Presumably MSFT isn't adding to Windows 7 any features that it expects to change how developers work or what applications will be able to do, or it'd be marketing the upgrade to encourage adoption beyond the seemingly business-as-usual tone apparently taken with the upgrade.
Both Snow Leopard and Windows 7 have been dismissed by critics as mere service packs to their predecessors, so the low pricing isn't hard to understand as a tool to drive adoption in the absence of universal excitement. The puzzle is why Microsoft would want to encourage a diverse array of legacy software when it might be pushing broader adoption of its most recent technology.
Perhaps it's related to Microsoft's position (or lack thereof) in the PC support ecosystem, where improved operating systems might be expected to yield particular benefit ....