You're comparing apples and oranges. Here's some apples and apples.
Size matters. Not size as in total HDD space used to install the game, but total size of what's left when you take out the game assets (models, textures, levels, videos, etc.). Basically, the engine and the scripts. Now, Fable has a lot of script files, 399 levels scripts, two quest script switch files, a config file that activates the starter quest script, two level files that activate quest scripts, two data archives that hold pieces of quest script information, one of those data archives even holds cutscene scripts, and then there's the executable that holds the core scripting that makes in-depth script modding impossible without source code that no one will ever see, perhaps hidden out of shame and embarrassment. These scripts, of different types, in several different places, are all held in place by a single binding force that I previously referred to as "super-glue". They're actually very sensitive, and this is noticed when messing with them. A single, tiny little error, seemingly insignificant, will melt away that glue and throw Fable's panties in a twist.
Yes, the different types of scripts are "purpose-built" and so cannot do spectacular things on their own. However, with access to the core scripts, for example, having them in a file separate from the executable (over half of the executable is the core scripts), then there would be no issue except for that one unknown compression and the unknown data in many of the files.
So, getting in the heads of the devs, we want to keep Fable's panties from getting tied up in knots. We want to check for script conflicts. Making sure that the scripts, no matter what circumstances the player is in, what order the scripts are called, will not cause the game to crash. Yes, the scripts are in a thousand places, but we can skip all of the insignificant/unessential scripts, like "useless rock goes here". After that, there's only a handful that needs to be checked. From there, there's only the issue of engine bugs, bad assets, and oversights. Most of those wrinkles are ironed out in small test sessions.
Oblivion. Scripts. They're all written in one language, they're all in one place, but there's 1700+ scripts, some huge, some small, and each one has the potential to break the game. That's a lot of checking to do, that's a lot of things that can be missed if everything isn't thoroughly checked out under a microscope, cross-checked with everything else, in every possible combination, and because of the capabilities of the scripts, a lot more is possible, a lot more, and that means more is involved in testing.
Oranges and oranges. Talking about modder satisfaction. What was good about Oblivion modders was they were given a studio-issue general purpose tool with which almost any kind of edit is possible. Formats were easy and made sense. Modding was condoned and promoted, not chased off of the official sites. None of this is true for Fable modders. Fable formats are among the worst that I have ever seen. Many of them, even five years later, aren't completely known. One of the compressions isn't even known. LionHead hasn't provided much anything that could be considered useful as far as format specs go, let alone a tool for the files. They don't promote modding. LionHead isn't completely to blame, you could also pin it on their higher-ups, those people, if you can call them that, that promoted Peter. And again, hardcoded core scripts means that without source, extensive modding won't ever happen. Aaand he shoots, he sco... no he really did shoot modder satisfaction. This so happens to be the case with Fable II, except there's more glue, worse formats, a terrible archiving system... think about it like this: Fable was the worst game when it comes to modding potential, and LionHead broke their own record with Fable II.
Bananas and bananas, game stability recap. Aside from the script conflicts, leaving just engine bugs, few and far in between in either Fable or Oblivion. They do exist, yes, but without making an extreme effort to find them, you won't. Grapes and grapes, game quality. Both games are good games, both are now old but there are countless people who still play the games, myself included, and each game has solid fan bases in online communities. Most of my dissatisfaction in Fable and Fable II is the lack of modder support, if I were not a modder and did not ever look at the games' insides, and did not take an interest in bettering the games, but was only just a player of the game, I'd have almost nothing bad to say about it.
I'm exhausted.
