In Visual Studio 2010, under Tools -> Options -> Text Editor -> HTML -> Formatting -> Tag Specific Options, there are options for configuring how the editor auto formats differe
Indeed there is no any significant difference between the two folders (Client and ASP.NET) from the VS's point of view. They exist just for convenience. The fact is that the tag is recognized only by its name and (luckily) VS ignores it's not a true tag. Therefore you can put subject settings in either of the folders. Even more one can create (what personally I did) another folder (called, for example, Expressions) and store settings there.
Concerning changing "Default Settings". If one wants to change settings only for a few tags then IMHO it should be better to create/change the rules for these tags themselves rather than changing the defaults (appears that h1-h6 rules are missing withing the default set of rules).