I thought this was interesting...
http://www.gamasutra.com/view/feature/2604/esrb_rating_distributions_and_.php?page=4
As always, the Nintendo platform stands out for its selection of games appropriate for nearly all gamers.
From the beginning Nintendo has wanted to attract non-traditional gamers with its Wii hardware and software. Perhaps as a result of the manufacturer's strategy, many Wii games have been designed to appeal to -- and therefore are rated for -- a general audience. Over 82% of the Wii catalog is either rated E or E10+. Only 3.2% are rated M, less than half the rate on Nintendo's previous console, GameCube. Still, that 3.2% is significantly higher than the rates on either the Nintendo DS or the Game Boy Advance.
Microsoft has announced its goal to court more casual gamers with games like Viva Piñata and Scene It! The distribution of ESRB ratings on the Xbox 360 is suggestive of just such a shift.
At this point in its life, over 54% of the Xbox 360 library is rated E or E10+. Compare this with less than 42% for those same categories of games on the original Xbox. It is also possible that some games which might have been rated T prior to 2005 are now being given the new E10+ rating. The class of M-rated games accounts for 17.6% of the Xbox 360 library, which is quite similar to the 19.2% of M-rated games on the original Xbox.
Finally, the PlayStation 3 has a distribution that is markedly similar to that of the PlayStation 2 and PlayStation Portable.
Almost exactly 47.2% of the individual libraries of the PlayStation 2 and the PlayStation 3 are rated E or E10+. Games rated T account for nearly 32% of the PlayStation 3 library compared to 38% on the PlayStation 2. The M rated games are a significant portion of the software on the PlayStation 3 currently: 21%, up from 14.8% on the PlayStation 2. No other platform, studied here has as high a ratio of M-rated games as the PlayStation 3. The two platforms with comparable numbers of M-rated games are the Xbox (19.2%) and Xbox 360 (17.6%).
Unique Company Signatures
With the exception of the GameCube, Nintendo platforms are all very similar in their distribution of ESRB ratings. That is, the GBA, Nintendo DS, and Wii all have about the same percentages of T-rated and M-rated games. It amusing to note that the one platform with a significantly different distribution of game ratings was also arguably the least successful.
The two Microsoft platforms are notable for their large proportion of M-rated games.
Sony platforms are also quite similar to each other. If it were possible to rerate the entire PlayStation 2 library to include E10+ games, its distribution might look much more similar to the PSP distribution.
The set of PlayStation 3 data consists of only 176 titles at this point, and therefore may change substantially in the near future.
The above comparisons show that each manufacturer generally has similar rating distributions across its hardware platforms.