I think the last response is true enough for a certain demographic of restaurant, but there are also a vast number of variables and scenarios, and you don't know which you're in for without just asking.
Your avg. bar will probably have inexpensive house wine that's undistinguished at best because they and their clientele are focused more on liquor and beer.
An inexpensive neighborhood pizza joint that focuses on food and doesn't have a sommelier or even a bartender, or much space for storing wine likewise will probably just get something inexpensive and mass produced to satisfy customers who just want a glass of anything.
Beyond that, a little more upscale and anything is possible. If the person in charge (chef, owner, bartender) has any interest in wine, the house wine could well be both decent and decently priced. I think one sees a bit more of this lately because of the rise of wine bars.
It is also true, as mentioned, that between technology and global warming, there is much less truly awful wine out there. (And much more bland but but sound wine.)
Back in the day, when I was working in restaurants, popular house wines were Sangre de Toro, simple chiantis, and various cotes du rhones (red and white). These were all good choices for accompanying hearty food, and good value to boot.
I've always found that if asked, staff will tell you what their house pour is and you can decide for yourself. Many places have even offered me a tasting when I show enough interest to ask. (The Mia Francesca restaurants have always been very friendly about both offering a short but interesting and rotating by-the-glass list, as well as having a decent house pour.)
So, bottom line is, if I'm just having a non-special meal and feel like a glass of wine, I ask what the house pour is, and then decide. What I don't do is just order "house" wine blind, without knowing or asking.
"Strange how potent cheap music is."