Is there any difference in the number of hours different generations and models of MacBooks take to "fast-charge" to 80%, or to fully charge?
All Apple products tend to finish the quick charge in just under 2 hours and reach full charge capacity just after 4 hours have passed.
Look at http://www.apple.com/batteries/ where this nice chart explains the charging curves in terms of voltage rise and current flow over time from empty to full.
As your battery ages, the charging does deviate from this curve and of course the 85 Watt adapter on a 15"/17" MacBook Pro is sending more current to a larger battery, but in the end, the stock new charging performance of all Apple products (iOS/iPod/portable) are designed to meet these times by changing the internal circuitry and power sources.
Faster charging is clearly possible, but degrades the life of the battery so my observation is that Apple controls the charge rate by having a charge controller that slows it down to meet these target times.