ClickBanks concern is with the refunds and/or chargebacks they are experiencing with the guarantee policies over 6 months, by the users of their services. Not necessarily under 6 months.
If a consumer were to dispute a charge to their credit card company, the credit card company would go directly to ClickBank. Not the merchant in question.
ClickBank is making a 6 month guarantee it's policy. If a chargeback request is filed with them after 6 months, and your web site states a longer guarantee period, there will be a problem.
It is also not a "higher level of service" issue as you stated. I'm positive there isn't anyone complaining or concerned with "higher levels of service". But let's not confuse "service" with a "guarantee".
Replying to an email promptly is considered a "level of service". Refunding monies for a poor product is a legality concerning your "guarantee".
And again it is still ClickBanks policy as stated in the notice they sent me and to others. Since you do not use their service, I can understand you being in the dark about the issue itself.