I've heard 'stan' is an acceptable alternative for 'staden' -- is this true or is it just a colloquialism-type-thing?
very sorry but your wrong, they are different ;)
i am half swedish so i will try and help you, stan is different to staden: they mean town and THE town :)
Does swedish not differentiate between a city and a town?
Not really. If we absolutely want to, there's the word storstad that can be used for cities. But we just don't use it that much.
There is "småstad" too, tracks pretty well with "town" I find, if you need to be specific.
Are there different words for city and town (one bigger, one smaller), maybe a diminutive for "en stad"?
There is storstad and småstad if you need to get specific. Storstäder in Sweden usually refers to Sthlm, Gotenburg and Malmö.
Keep hearing "#en är" as "#erna"
i always hear staderna stor
When people from sweden talk swedish, swedish words hear often as if they are connected.
Why does it not mean: "The city is "big""?
Why quotes around big?