Yes. No poles = no latitudes = no temperature variation.
The current temperature variation logic doesn't match reality well, as the difference between the hottest and the coldest time of the year gets greater the further you get from the equator, rather then reversing half way, as half a year of darkness followed by half a year of sunlight can result in rather significant differences despite the sunlight having to pass through a lot of atmosphere [which might be what Toady simulates with the decrease from the mid latitudes], but in the game world it's the game world logic that rules (and nothing says seasons depend on the tilt of the world's axis as it rotates around the sun anyway)...
I feel like your logic is a bit off. Think of it this way: When you set the world to have no poles the sun is shining on the world equally all the way around. When you set it to just one pole (lets use the south pole as an example) then, sort of like earth, the sun isn't really ever touching the south pole all the much, so it's colder. If you set it to two poles, like earth, then it functions like earth does. So a world with no poles means no temperature variances.