Kudos to Heady for pointing this one out! IMG has posted an interview with Halo Project Leader Jason Jones, and it's not to be missed. Here's an excerpt:

IMG: Any particular reason for the Marathon logo, or is it just for kicks? Is Halo somehow tied to and/or an extension of the Marathon series?

JJ: I'll say this: Observant fans of our games will note that certain themes tend to run through our games. For example, the sword Durandal (from the Song of Roland ) first appears in Minotaur as a magic sword and goes on to become a central character in Marathon. There are many other examples of common themes running through our games.

Lots of new info for the FAQ, too... be sure to check this one out!