There is a nice little blog that I found the other day, courtesy of one of the other blogs that found it first (there were so many). It's called the Absorbascon after a device in the older Hawkman comics that contained all of the knowledge on Earth. The Absorbascon blog is a wonderful fan-blog oriented towards the DC comics universe (among other things). He's only been at it for a month or so apparently, but he's got a ton of posts there already.
I wish that I'd found it earlier, though, because there are some great posts on a model for DC's heroes that he calls the "Dynastic Centerpiece" model, involving basically a central character as the centerpiece of a dynasty with other characters filling in roles around the central character (like the Kid Sidekick, the Female Version, the Super Pet, etc.)
It's a great little model, but its hard to make it work in the general case. I think that the author is conflating two different types of breakdowns for superheroes into one model, and I think that's where the difficulty lies. I've thought before that DC has two different types of models for their superheroes. The first is the "Family" model - the hero at the center with all of the various different heroes of the same type surrounding him. Batman and Superman are the classic examples of this, with their various younger versions, female versions, pets and whatnot. The Marvel Family is another good example of this phenomenon.
But, when you look at some of the other heroes, it gets tougher. The Flash barely fits the model at all, and others like Green Lantern or Hawkman really have to be stretched to fit it. These heroes follow more of a "Legacy" model - the hero as the most recent bearer of the standard for a particular costumed identity. This is the model that really comes from the Julie Schwartz-style of superhero revamps that occurred in the 60s, along with the merger of Earths 1 and 2 post-Crisis.
Flash fits the "Family" model better than many others because of the Waid expansion of the Flash Family during his tenure on the book in the early 90s. I would guess that Waid is a fan of the "Family"-style of DC heroes and (consciously or not) saw a way to fill out the Flash pantheon a bit by expanding on the idea of a Flash Family.
Marvel has never really played their heroes in this manner - there are no Legacy heroes at Marvel, for example. Captain America is the same Captain America who fought in WWII, not a new one. Namor is the same Sub-mariner from the Golden Age. The Human Torch is different, but its not like there's a Human Torch legacy that gets explored in the Marvel books. Any "families" that exist are more like the Fantastic Four or Power Pack - constructed as a specific superteam and not spun off from a central, popular hero.
Marvel has been branching into the ideas of Legacies and Families, however. In the last few months, Marvel has introduced (another) female Spider-man and a female Wolverine - possibly giving the start of a Spider-man Family or a Wolverine Family. Spider-man has a Legacy on the Marvel version of "Earth-2" also, with the ongoing Spider-girl comic book. The Hulk has had a female version of himself running around for a while, though they are rarely played up like a "Family" style book. And now they have a whole group of "Kid Sidekick" versions of Avengers characters in their own book. All-in-all its looking like Marvel is considering the Legacy and Family ideas more and more. I suspect its for the same reason they grew at DC - spin-offs of popular characters can be great money-makers if they are done right.
 The MC-2 Earth maps well as Marvel's version of "Earth-2", a world where their prime superheroes aged in near "real time" and have passed on their legacies to their children. Its also the private playground of Tom Defalco, much as Earth-2 was often the private playground of Roy Thomas back in the day. I always consider the "Ultimate Earth" to be Marvel's version of "Earth-3" - the world where the heroes are villains. In Marvel's case, its more like a world where the heroes are jerks, but a strong case can be made that Millar's Ultimates could be considered more villanous than heroic.