Is there any reason to assume they are “so focused” on it? Keeping an eye on unit or per-weight prices is somewhat conventional and pretty easy—at least I think most major grocery chains around here include that info right on the sticker.
At least where I'm at they're legally required to include that info and they appear to comply maliciously whenever possible. Sometimes it's slightly wrong. Often the unit of weight changes between items of the same sort. It's absurd.
You did not understand the comment. The person is talking about units per dollar, not necessarily calories per dollar, or anything about health. If I can buy one sponge for $1.25 and three sponges for $3, for example, I prefer three. This has nothing to do with how many calories are in a sponge.
With your focus on calories per dollar, do you also get supplements? Which ones and where?
Why are you so focused on this?