It sounds like what you really mean is that this is not a product which you benefit from, because you work from home and your house is actually continuously inhabited most days; it's an amusing combination of arrogance and naivety to assume that your lifestyle is the only valid option.
Beyond that, you're completely missing the point about a smarter thermostat: the savings don't come from the temperature outside is -15° and your heater is running almost constantly. You have to deal with that by adding insulation or living in a colder house. Where many people can save money is waste: when the heating or cooling would have run without benefit – e.g. it's 40° outside and you're paying to keep it over 65° but it'd really be perfectly fine if it drifted down to 50° for the 8+ hours in the middle of the day when everyone's at work. A serious miser will religiously turn it off before they walk out the door but most people won't. Many people even leave the thermostat set at a comfortable temperature because they dislike coming home to a very cold/hot house.
Those people are the ones who will benefit the most from something programmable but unfortunately most of the devices on the market have horrible UIs and none of the $30 ones will do things like detect when you aren't home, which is significant for people who don't have rigidly predictable schedules. Again, it doesn't have to be a game-theoretical optimum – only better than what most people are doing now.
> Unfortunately my heating bills over a very long term only average maybe $100/month, which I'm sure sounds insane to coasties
Head to New England and your new neighbors will complement you on your frugality, as most people have heating bills 4-8 times that high in the winter. Toss in, say, a spike in heating oil costs and anything which reduces inefficiency starts to look pretty cheap. Hint: none of them had McMansions, either – it's just cold during the winter in Connecticut.
> So I can save about $1/month or $12/year. At $300 retail, it'll pay for itself by 2039.
Even worse, most will be purchased using a 30% interest rate credit card, making payback time infinite. The 30% interest on the credit card to pay for the $300 thermostat would be $90/year but I'm only saving at best $12/year. Whoops.
When you need to make up numbers so the math makes your argument seem less arbitrary it's time to accept that other people are allowed to make decisions in life without your approval. You're overstating the purchase price by nearly 25% and assuming the worst possible purchase method – and you're doing that for an amount which the average American household spends on cable tv / internet / smartphones every couple of months.
> The final killer problem is I intentionally don't live in a McMansion so I can have a better lifestyle, such as not shivering in the winter. I've already decided to own a 25% smaller house to save 25% on my heating bills, I have absolutely no interest whatsoever in saving 10% on my bill by shivering. I'm not paying thousands of dollars a month to shiver in a house when I could be warm and toasty in a hundreds of dollars a month apartment. Nope not happening non-starter totally uninterested. Selling snow to eskimos. Nope.
You do seem to need a lot of external validation for your decisions. Hopefully the smug feelings will keep you warm.