Yeah pretty much, $4 is a pretty good price for that distance. Where are you all traveling to that you need to go from Puerto Madero to Belgrano every day? Seriously, I was hearing this stuff when I was living there before and it confuses me.
Taxis are cheap here compared to most other major world cities, but if you compare them to buses, subway they are expensive. And, if you take in to account annual price rises the last couple of years of I swear 40% p.a and of course local wages, they are not comparatively cheap.
For example, if I want to take a taxi to work for some reason (running late, need to arrive quicker, dont feel like being packed like a sardine on the bus or waiting for half an hour while 10 full buses pass without stopping), it costs me 40-45 pesos (from libertador / scalabrini) in to border of centro / Puerto Madero.
Or, if I want to go to South PM for dinner, 2 weeks ago it cost 60 pesos. A bit over a year ago - under 40 pesos.