I’m in Massachusetts, and we kinda have a mix of everything. I live in a condo on a concrete slab that was built in the 70s as a neighborhood of duplexes rather than what people think of today when they think of condos, while my parents’ house has an unfinished, root cellar style basement in a flood zone, and a friend of mine recently moved back into his mom’s furnished basement a stone’s throw from where I live. There’s a house near my parents that even had to put their front lawn up several feet with a concrete foundation so that they could put in the septic system above the aquifer.
As for rowhouses, I don’t know much about them, but I assume that they’re usually on a slab with no basement because they usually have 2 households in them with 2 separate entrances for them. The more fancy townhouses you see, like the brownstones in NYC or the ones in Boston, might have basements since they were built for the wealthy and are single family homes that even had servant’s quarters, but I’ve never been in one to see. There’s a cool section of Boston with townhouses that was originally built to attract the wealthy, and there’s streets behind the buildings simply named Alley #1, Alley #2, etc. because they were only built to allow the servants to move out of sight of the wealthy.