After nearly 40 years of snowshoeing experience, without heel lifters, it never occured to me that anyone would consider them anything more than a marketing gimmick. Much less did I anticipate that my opinion on the matter might be offensive to anyone who had purchased snowshoes with this option. Given your defense of heel lifters, I suspect you felt my comments were inflammatory, and I apologize, DebW.
From your description, I understand that heel lifters raise one's heel off the ground, so that the foot is kept in a more level plane when climbing uphill. This would be like having a large wedge under the sole of one's boots. By keeping the foot in a level plane (while going uphill), stretch of the calves and associated tendons are minimized.
I can't help but wonder, what do you do in the summertime?!!