A wine snob took me to a wine tasting many years ago. There are of course plenty of different tasting wines. Some smelled like an old sock but tasted nice. Some smell nice and taste horrible.
Most restaurants that serve a house wine have probably spent a bit of time and experimentation in choosing the least offensive or most well accepted wine that costs them very little. And of course fancier places pour from premium bottles and call it the house wine.
A friend of mine (one of the guys we used to have those dinner parties I wrote about above) owns a couple of restaurants. He was very clever in opening his first place though. Got a great location in a trendy area (and somehow got a great lease rate but spent a fortune in building it out). They serve coffee and danish stuff starting at 5 am, free wifi etc. Around lunch time they serve wine and after 3 they turn off the wifi and focus on selling glasses of wine and small plates of food until after 1 am. The mark-up on some of that stuff is incredible, like, costs him $2-$4 for a bottle and he charges $8-$12 a glass. And up from there of course. Huge selection. So I guess people like wine. No hard liquor. I imagine the markup on coffee and danish is likewise huge. Personally now I hate spending money on wine in a restaurant knowing their margins are so massive.
Occasionally I do pay for a bottle of wine in a restaurant and the bottles they charge $60 for can be gotten at the local liquor store for around $15. I'm sure the restaurants pay less than the $15.
The standard restaurant markup for a bottle is 100-200%. Lower than 100% is a rare bargain; more than 200% is gouging.