Several years ago I noticed that (quite often) the best selling and highest profile games in a series tended to be the third or fourth game in the series ...
The reason I came up with for this was that publishers don't push a new IP all that hard because marketing is expensive and you don't want to take away attention from "More reliable" games. If the game sold moderately well it would get a sequel which had a larger development budget and the publisher would push the game harder to try to expand upon the success of the first game. Eventually, after the second or third game is really successful, the game becomes a high priority for the company and this results in a focus on making the game as high of quality as possible and releasing it with the biggest marketing push possible, and when combined with a solid word of mouth campaign from existing fans the game sees explosive growth in sales.
We haven't seen much of this with the HD consoles and I suspect that is because even games of questionable quality cost so much to develop that publishers are puting as much money towards marketing as they would typically reserve for the second or third game in a successful series. When you take a game like Gears of War which had as large of a marketing campaign as I have ever seen people may be under the (false) impression that it is easy to make a new IP into a multi-million selling success; which in turn makes people assume that new IPs which fall short of this mark are unsuccessful or "flopped".
With games like Zack and Wiki, No More Heroes, Boom Blox, and even Little King's Story I wouldn't be that surprised if publishers are looking at these games in a much more conventional way. With sales of 250,000 (to pick a number) they know that there is a market for these games and they can aim for sales of 500,000 units with the next version and potentially 1,000,000 after that.
