Patrick Washburn: splash:
What was the purpose of mentioning that by example if not to slow the Subies down?
Despite our best efforts to write Suby's out of existence, 
this was a response to a letter written for clarification. We have formed a secret "Subaru" sub-committee though, to brainstorm some more unsolicited anti-Suby rules changes that will soon be forthcoming. 
In all seriousness, the clarification request was framed in a different context. I agree the wording in the original rule can be confusing when applying to various specific conditions. I think you'll find that the intent here is to clarify that heat shields that are attached to an exhaust component are allowed to be removed along with that exhaust component, and need not be modified and re-attached onto the allowed alternate exhaust component. In other words, heat shields attached to an exhaust component are part of that component. Other heat shields (such as turbo shields or shields that are body mounted) may not be removed, but may be modified the minimum necessary to fit an allowed component.
While I do not believe this is a real attempt to get the Subarus out, how else were we supposed to read it when it specifically mentions WRX/STI?
The wording for the clarification was poorly chosen (as was the wording for the emissions one if I remember right). As it is, we are not allowed to touch the stock turbo heat shield in ANY WAY because if the turbo heat shield is not considered part of the exhaust, it is then part of the turbo. This makes any non-stock downpipes illegal because they ALL require trimming of the shield to fit. There is no middle ground as it is. If it's an exhaust shield, it can be trimmed. Since it is not, it can't be touched. Now, we can MAKE custom downpipes that can fit, but that's not exactly a "common modification", now is it?
This also has ramifications as a precedent for SP since you can't touch the turbo there either. If the shield is a part of the turbo, then the HKS (or a custom DP) is the only DP that would be legal on a Subaru there.
If the TRUE meaning was as you say, then you need to add the part about "Other heat shields (such as turbo shields or shields that are body
mounted) may not be removed, but may be modified the minimum necessary
to fit an allowed component."
Oh, and be more careful next time y'all decide to "clarify" something... :)