Casual titles normally spike during the holiday seasons. It's a misleading idea that casual gamers only buy casual titles. In reality casual gamers buy big brands. Mario, Zelda, Guitar Hero, Rock Band, Wii Fit, ect. This is why you see these games selling well throughout the entire lifecycle. Nintendo has a large section of casual gamers and they will buy brand titles with their console and throughout its life.
However in holiday season, casual titles are usually picked off by buyers trying to find a title that they think someone might like. Considering most casual titles have names that kinda rip off a popular brand(such as Carnival Games, Game Party and SmartyPants) these are the titles that sell the best. And then eventually they become top brands and sell throughout the rest of the year.
While core titles sell well in the first few weeks and then only depending if they gain huge brand appeal will they stay alive. Now this doesn't mean casual titles that don't have big brand can't sell well outside of a holiday season. It's just most trends show that casual titles enter at a steady but unexciting pace and then will either be picked up and exploded during the holidays or stay the same. This is why you saw Wii sell so much software in December compartively and why software has continued to stay heightened afterwards.
Always good to break stereotypes. Those are casual gamers buy big brandname titles because they are mainstream buyers. They buy casual titles really at random. Most early adopters of casual titles are probably core gamers. Casual titles sell steadily throughout normal part of the year but may explode during the holiday season or may fade before getting there.
