Fran - Mel probably has a much better explanation but let me give it a shot.
The 'honeymoon period' isn't really referring to
weight loss as much as it's referring to
muscle gain. It's a well-known phenomenon (though I can't cite you any scientific sources at the moment) that a beginner lifter can pack on lots of muscle
and lose fat simultaneously. That's why the first six months of lifting are also known by names like the Golden Time etc. - it's when you're going to see your largest muscle gains in the shortest period of time. And it only happens that one time - the first few months that you're lifting.
After those magical six months or so, muscle gain slows down to a normal pace: maybe (if you're lucky) 4 to 5 pounds a year for a woman with rigorous training and totally 100% clean nutrition. And after those wonderful first months, it becomes difficult, if not impossible, to add significant muscle while operating in a calorie deficit. That's why you'll hear bodybuilders talk about mass building or leaning down, one or the other but not both.
So the honeymoon period really isn't about when you're going to lose weight the fastest, though I know you're aware of the connection between muscle and weight loss. It's when you're going to be putting on muscle the fastest. You're right, a faster metabolism is always a faster metabolism and that's the result of the muscle added during the honeymoon period.
I found this to be true myself during the year that I lost weight ... I packed on a ton of muscle for the first six months and then lost some (but not all of it) as I got down to my goal weight. The muscle that I built during my honeymoon period let me end up at goal with eight more pounds of muscle than I started with - a good thing!
I'm not sure that I'm answering your question very well, so we'll let Mel come along and explain it better!