Now, legal activities are NOT more expensive in real life, but in the game, some are. That makes no sense. And while we reached a draw at the illegal stuff, at the legal stuff the mechanic makes zero sense. So on the whole, it makes sense in 25% of the cases, while making sense on a fundamental level would be 100%. 25%, that's not a lot of sense.
If you're a rich king people expect you to throw a better feast than a poor count. Same for tourneys, fairs etc. So it costs more. As for pressing claims, in a rich realm people expect higher bribes because everyone's income is higher, so again it costs more. Think about it: If you make £20,000 a year you might be willing to risk your job for a £50,000 bribe, but if you make £2,000,000/year you'd laugh that offer out of the room.
Seems reasonable to me.
Or, if you don't accept that: Game balance.