However, if my laptop is old and slow, and I'm already in the market for a new computer, I can easily be convinced to buy the computer with the "bigger numbers". Buying i7 instead of i5 only a small part of the full price, so why not?
When I think about my daily work - it is very multi-threaded:
* parallel builds
* video running in chrome
* a zillion tabs open
What I really care about is battery life.
I would be exceptionally surprised to see any of the higher-budget games running on a single thread. Low-budget indie games less so.
Personally, I've found that a good benchmark for "what is happening in most games" is the lowest common denominator - consoles.
Having said this, you might be arguing that it's hard to split everything out equally in a game - but it's far more likely that threads are created for the stuff that can be - physics calculations, sound, etc. (the stuff that might have, in the past, be split out to dedicated hardware)
They are, though slowly. The skylakes are a bit faster than the broadwells are a bit faster than the haswells, etc.
The old CPU's sharing a name with the new CPU's makes them sound like they're still up-to-date. Which I guess is great for making you feel better about your old device? This seems potentially detrimental to sales though, so I still don't understand the impetus for marketing them like that.
It's an entirely usual thing to maintain marketing names between generations because the marketing name is rather a description of the target audience than of the concrete feature set or technical specs.