Kabouter Games
Explorer
There's no reason why the Pope has to be a level 20 adventuring cleric. In fact, being an adventuring cleric ill suits a priest to be Pope. It's far more useful to be skilled in the internal politics of the church. It's infinitely more useful to remain close to the seat of power, where you get to know people, manipulating favor and patronage. Bimbling all over the countryside smiting heathens does precisely zero to improve either skill set.
I've been thinking about this one a bit more.
If anything, the high-level adventuring cleric is a direct threat to a non-adventuring prelate. The adventurer directly and obviously manifests the immense power of the deity, where the prelate sits in a room somewhere and, unless something dire happens, is comparatively invisible. People start to wonder about why they listen to the prelate. People are people, and religious people have an alarming tendency to turn such affairs into The Life of Brian. If anything it leads to a schism in the Church.
Say, that sounds like an interesting high-level campaign. But I digress.
Those of you who remember the details of AD&D will remember that EGG et al envisioned the strongholds and "name" level ranges to be excellent ways to urge characters into retirement. They start getting pulled every which way but the path of adventure. It's hard to just chuck it all and go on a quest to loot a dragon's hoard when you have thousands of people clutching their gourds and shoes, expecting you to challenge the existing hierarchy, when you've got a bunch of apostles - another hierarchy - springing up around you. Your god might have some choice messages for you. You might end up crucified, or on the end of an assassin's poisoned knife, either way a victim of the prelate's pragmatism. Easier to just start a monastery somewhere, where you can retire from the world and contemplate the mysteries of your god.
Anyway, I think it's interesting.

Cheers,
Bob
www.r-p-davis.com