I recognize that any TL that has good payment history is a benefit to one's credit worthiness. However...
How does an AMEX charge card help FICO scores if it doesn't count towards utilization?
Does AMEX contribute to the diversity of one's portfolio because it's different kind of credit? (And what kind would the be?)
Because it doesn't count you can run all your bills through the card and if they happen to post it has no impact on your report. Where as if it happened on a regular card you would take a score hit. Also other companies and manual reviewers will take note that you have AMEX on your report and that they are in good standing. If you always PIF before the statement cuts without fail the charge card may not help, buit charge cards will grow with you and you won't have to tie up your other credit with charges that will be paid off at the end of the month anyway and that can be important when you are rebuilding and just starting out, When I just had low limit cards and only 3x major cards tieing up 50% of my total CL with bills would be bad.
FICO wise it counts the same as other revolving tradelines as far as payment history and bucketing goes AFAIK; however, it simply isn't tabulated in the revolving utilization metric as James correctly points out, at least under any "modern" version of the FICO model. '98 and earlier utilization on charge cards still applies.