Picked up a pure one oil filter the other day, and the application book did not have 2006s listed. Since it seems they've been the same filter for the past few years for both the 2.0 and 2.5 motor, I figured it'd be a safe bet.

Are they the same?

Same yep... Filters from my wrx even work on my 94 leggy :)

Subaru has recently standardized on a single filter for the Imprezas; however it is smaller in diameter than some of the filters used earlier. Especially for more recent turbo models, Subaru wants to make sure there is enough separation between the filter and nearby exhaust tubing.
You may want to compare the PureOne filter's diameter with that of the current Subaru "A100" filter.

subaru has changed to only 2 filters now 4 cyl and 6 cyl and the one for the 6 will work on the 4