Maybe... i dunno. Market Share doesn't seem to effect sales that much for core games. I mean look at most series...
Usually the first game out for a franchise is the best selling one.
It's usually the unconventional titles that are new IPs that start off low and then raise in sales as the gen goes on.
Most people I talk to about the game either say that they are waiting for a price drop on it or they bought/are buying it used. Used games don't really go into the sales data (from what I've understood at least). Although, there have been major sales for Ratchet & Clank: Quest 4 Booty through PSN. No confirmed sales figures but it seems to have sold well considering that it made it into the top 10 for the year with an August release date and no bundling/deals on it.
There are also people who were waiting for a second Ratchet game or a Jak game to come out to get the PS3 since it does carry the hefty price tag.