I've had a beer ferment all the way through without seeing a single bubble in the airlock. It was in a bucket, so I couldn't see any krausen either. I'm not sure if it just fermented very quickly (i.e. overnight), as I did check it several times during the first week, or had a leak on the lid. I checked the lid several times, and pushed as hard as I could all over to make sure it was seated well. I figured I would just ride it out as it was a beer I wasn't super stoked about. After three weeks, I opened it and my FG was right where it was supposed to be. I've used that bucket before and after without problems, so I'm not sure what was going on.
All this to say RDWHAHB. A lack of airlock activity does not mean the yeast aren't doing their job. It doesn't sound like you did anything to screw it up.