I think these time estimations are a bit silly. I understand they feel the need to explain the value proposition. I also understand that for some people the goal is to obtain the longest, most time-draining game possible, so they don't have to buy any other games for a while.
But I feel that:
A. These estimates are very difficult to project - it depends on how you play
B. Even worse, they glorify quantity > quality.
Some of that comes down to my playstyle. I'd rather play a great game twice, then play a very good game for a longer amount of time. I'm compelled to play again if the experience is fantastic.