Actually.... *dons Minecraft historian cap*
First we got rails and carts. This was great for going downhill but abysmal for going uphill unless you had a nice downhill first. Trips down into the mines, then back up? Madness!
Then we got the powered cart. We got visions of being able to use one cart to push another cart out of the mines. However this proved less than ideal since a powered cart could only push a loaded cart at a snails pace, it was faster to walk out of the mines than it was to take a cart.
Then someone found a glitch whereby two carts which were on rails side-by-side, would become both simultaneously locked to one another and push each other at the same time. All of a sudden it was possible to get a cart up to max speed in about 4-5 rail lengths. These were called
boosters. People were able to
get out of the mines in record speed, travel large distances without problem. Until the dark times.
Those times came when Mojang decided that the glitch should be removed. As compensation we were given powered rails. However, the rails proved about as tepid as the powered carts before them.
Now, you can argue that having powered carts with powered rails isn't needed, but there are pros and cons to each. Besides, if all you see in Steve's Carts is powered carts, then you're ignoring the bulk of Steve's Carts. Personally, I don't even have it installed in my world; just as I have turned off all rail related portions of railcraft. I just don't do minecarts since Mojang removed boosters. If you watched the video above you'll note I had 3 whole boosters to travel from near bedrock to my base at around y60. To do the same with powered rails would take right around a stack of gold. Even in modded minecraft you'll be hard pressed to get me to dedicate a stack of gold to a single run of rail. But a powered cart, running off of charcoal, which is renewable? Huh, all of a sudden it isn't so bad.