philon,
A palace does store 8 units of wine but uses 4 each month, so it can run out of wine in 2 months (just like furniture or oil). A grand villa does store 8 units of wine, but any other villa stores only 4 so it can also run out of wine in 2 months. As far as I can tell, a house tries to store between 4 and 8 units of each food for each resident. Therefore, if markets are kept supplied, a house with 3 foods should store at least 2 years worth.
Tomek,
Your consumption numbers are almost right (a full luxury palace requires 1188 total food per year, not 1200), but not the market buyer numbers. On each trip, if she can, a market buyer does collect 200 of a non-food good or 800 of wheat, but only 600 of another food. But more importantly, if she needs to, a market buyer (unlike a Pharaoh bazaar buyer) will leave to get more food/goods almost immediately after returning from her previous trip, and can therefore make several short trips per month. The 2 markets in the luxury block in my Happy Massilia easily support 8 luxury palaces and could probably support several more (with buyers going 16 tiles each way (cutting corners) to get one food, 14 tiles to get another food, and either 5 or 7 tiles to get anything else).
goonsquad,
If market buyers ever have to go a moderately long distance to get at least one of the foods or goods, then Tomek's suggestion is likely to be correct. If not, then I'd bet on philon's suggestion. For stability, you should ensure that for every house, there is at least one market, such that the longest time between visits to that house by that market's trader is less than 2 months. If that isn't the case, then it's likely that every now and then, a house will go too long between visits by a market trader and will devolve due to the lack of furniture, oil, or wine. Having lots of markets makes that less likely but still possible. I suggest that you figure out what is going on by carefully watching your city and checking a large palace just after it has devolved from a luxury palace (or better still, a luxury palace just before it devolves) to see what good it lacks, then checking the markets to see whether they have run out of that good.
[This message has been edited by Brugle (edited 10-30-2003 @ 11:32 AM).]