While we would normally discuss these things, I think we can safely put it in here as an official house rule. In any event, I am putting this up - feel free to argue, but I think it should stay. 
Weapon and Armour Proficiencies in Ravenloft:
For characters hailing from domains with a culture level of 9 (eg: Dementlieu, Lamordia, Paridon, etc.):
Pistols are no longer Exotic Weapons - they are counted as Simple Weapons.
Muskets are no longer Exotic Weapons - they are counted as Martial Weapons.
Thus, characters like Rogues, Clerics and Sorcerers (for instance) from these domains may begin play with proficiency in these weapons as they are common enough for training in their use to be widespread.
For characters hailing from domains with a culture level of 8 (eg: Borca, Invidia, western Darkon, etc.):
Pistols are no longer Exotic Weapons - they are counted as Martial Weapons.
Muskets are still considered Exotic Weapons.
Exceptionally, as firearms are slowly coming into prominence in these domains, characters from Culture Level 8 domains may purchase Exotic Weapon - Firearms even if they do not have the standard prerequesite of +1 base attack bonus.
Characters from these dominas, then, gain an easier access to firearms, which are making an appearance on the scene, but not so much so that the other realities of these domains are lost. For instance, the bastard sword is, properly speaking, a culture level 8 invention, as is full plate armour in all it’s glory. This rule somewhat helps to highlight the liminal position of culture level 8 realsm.
Conversely, certain armour and weapon types are uncommon at best in certainrealms and as such, characters hailing from Culture Level 9 realms do not begin play with Heavy Armour or Tower Shield proficiency. The DM may also rule that certain heavy weapons, like bastard swords, greataxes and greatswords may be unavailable to the character as well and therefore may be beyond the character’s ability to use without purchasing these proficiencies as Exotic Weapons. (So, Greatsword would become an Exotic Weapon for a fighter from Mordent, say.)
Alternately, any character having lived in one of these domains for at least a year can be considered to come from such a realm if they have spent that time there before character creation.
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Give me your feedback, but I think this, as a general rule, prety much covers the main points of weapons and armour in Ravenloft. With a list of weapons by Culture Level we could really pin point it, but that’s too much work for too little payoff at this point.