Ah, re-reading the section on capital, I can see how you got that impression. But no, that's not the only way to increase scale, not by a long shot. I wrote that chapter of the PHBII btw, and it's based on stuff I've used in my home games for years.
To increase scale, all you need to do is keep your capital at maximum value for a set number of months. You can do whatever you want during those months! Beatify a saint, assassinate a duke, trade with the dragon emissaries, build a new road - anything. As long as your capital doesn't drop below its maximum value for the month, then at the end of a number of months depending on your current scale, you go up one in scale.
There are lots of ways to gain capital. Loot donations are one, of course. Others include actions like Trade, Harvest, and Plunder. Trade is especially important. Being friendly with an NPC (or PC) trading company can really benefit you. Frequently in home games, the PCs woo trading company officials with wine, party invitations, gold, and bugbear toes (a delicacy) to get their favor. A little Trade can go a long way for capital funding purposes. Also, capital can be a treasure reward for adventuring. Perhaps at the end of an adventure, a PC finds in the frost giant jarl's silver urns not just rubies and platinum but also a deed to a copper mine. The mine increases any organization's capital by 2 for as long as it is clear of monsters (cue adventure hook music...).
So, the bottom line is, yes, there are many ways to go up in scale without sitting idle! Hope that helps!
