It turns out there’s one other tiny difference between the Pixel and Pixel XL that we previously didn’t know about.
The smaller model maxes out at 15W charging speeds, coming up short of the promised 18W originally listed in Google’s marketing materials. Android Police reached out to Google, which confirmed that indeed the Pixel charges at 15W. The tech specs have been updated on the official Pixel page.
The issue was uncovered by prolific Android tester Nathan K., who shared his findings on Google+.
It sounds like nothing was intentional or malicious here. Most likely the Pixel team dropped down the spec from 18W to 15W for the Pixel and that detail was omitted in the official marketing materials.
The impact on you: In practice this means yes, there’s a charging difference in capability between the two phones. Given the difference in battery size, and the reduced charging speed as the battery fills up, it's not likely to make a noticeable difference.