His job is a very big deal to him, especially in these tough economic times. This fear causes men to (re)focus on their career/job. As they put their attention to it, other things suffer from a lack of attention — family, relationship, etc. He's probably not doing it on purpose, but it leads to women asking why he doesn't care or put effort in any more.
The rub: She doesn't want to tell him that she feels he's dropping back, because then his renewed effort isn't "genuine" (read: he didn't think of it himself, so it isn't him wanting to).
How she can help: Acknowledge the issues and the stress that accompanies them. She might remind him that you are both in this together. If life throws a curveball, she'll be there — with him and for him. At the same time, gently remind him that he needs balance. Jobs and money might come-and-go ... but she is there and that is where his effort needs to be also.