Martin Pitt had been at Canonical for 12.5 years while the other developer leaving was there for 11 years: Daniel Holbach. Daniel had been with Canonical since 2005 and served as a developer on the desktop team, founded Ubuntu's community teams, and then in the past few years had been working in community management and related community/relations areas.
Holbach wrote on his blog, "In the last weeks I had to realise more and more that I need a long break from everything. I therefore decided to move on from Canonical, take some time off, wander the world, recharge my batteries, come back and surprise you all with what’s next." While Pitt is joining Red Hat, Daniel hasn't yet decided where he's going to pursue employment next but sounds like he wants to stick around the Linux/open-source scene after taking a few week Internet-free break.
Good luck Daniel with your future projects!