The Bethesda-style RPG is built on putting the player character in a painstakingly detailed world and letting them run wild. Touches that add to the believability include NPCs with schedules, day/night cycles, and an unwavering devotion to keeping the player within the first person view point. However, not all of the systems put in place to encourage immersion translate into good gameplay.
In their two recent Elder Scrolls and Fallout games, store owners only keep a limited amount of money on hand at any given time, lending credibility to their existence as real institutions. None of the stores I shop at regularly has unlimited money behind the counter. Unfortunately this is one place where realism is more of a nuisance than a system that adds to the immersion.
While these games do a great job building their own realistic worlds, they contain plenty of unrealistic mechanics. All broken limbs can be mended and all health regained from merely sleeping for only one hour in a bed. In Skyrim my blacksmithing can be maxed out by making dozens of iron daggers over and over again. Unless I'm playing hardcore mode in Fallout: New Vegas, I never need to eat or drink.
If all of these inconsistencies exist in game, why do the vendors have a currency limit? All this mechanic serves to do is inconvenience the player when they try and sell a mountain of loot after an adventure. If the store owner runs out of money the player has to either wait a few days for the money to regenerate or go to every shop in town in an attempt to unload the spoils of dungeon diving. If I wanted a game where selling items is an adventure unto itself, I would play Recettear: An Item Shop's Tale.
This is one mechanic where Bethesda would not be faulted for putting gameplay over realism.