Ubuntu is aimed at beginners and people that don't want to fiddle around (too much). Earlier distros were very very good and very useable compared to others, so they attracted a lot of users. When Vista came out there was an influx of Linux newbies.
At some point Canonical decided they needed to make money from Ubuntu, so deals like the Amazon search come in. Obviously they're still aiming for the goal they were originally looking for (an easy to use distro for people to switch to) but their actions are alienating some of the more technical users who wanted a quieter life compared to other distros.
Unless something changes to retain the more tech savvy users (and those users that have grown to be more tech savvy because of Ubuntu's low barrier to entry) I wouldn't be surprised if we see a brain drain in the Ubuntu community as the more technical flee to Arch, Debian and Mint.