Howdy,
QUOTE (dailydriver @ Jan 17 2008, 02:05 PM)

UNDERSTOOD!
I was just asking as to what their motavation/rationale was for this given rule??
Flip it around to understand the deal... Why would the allowance have been given?
The way the rules have grown is by all us members coming together to agree on what we should allow as changes on a stock-from-the-dealer vehicle. To have an allowance in the book, someone (or, more accurately usually, a whole bunch of someones) need to have gotten together and all wanted that allowance.
I expect that rear end diff covers aren't a highly requested item and as such, not many requests have been made to allow it.
This is the "if it doesn't say you can, you can't" approach to rules. I think in general it works pretty well across solo (you could make an argument it shouldn't be that way in DM/EM/AM though).
The other approach of saying something like "you can do whatever you want, as long as it doesn't affect performance" doesn't work quite as well because everyone has a different idea of how much something affects performance. For instance, solid metal motor mounts don't affect performance much _to me_, but others disagree.
Nowadays, getting new allowances to a mature ruleset is hard as heck. Look how long subframe connectors took, and that's something people have been asking for for YEARS. Lots of folks are against new allowances just on principle as they feel that every new allowance is one step further down the modification path and we're already too far down it. Then there's the folks that are worried about unintended consequences (see also, electromotive systems worth more than the car they're on, etc.) of a rule that seems benign today.
Anyway, to summarize, nobody sat down and considered every possible modification and decided to allow it or not. They sat down with the stock vehicle and decided what to change. And a diff cover isn't a high priority item for anyone.
Mark