JPEGs generated in-camera tend to have a little sharpening applied as part of the process. RAW files do not, so they tend to be "softer" by a bit.
So you may want to sharpen them in Aperture.
It's very easy to do, you just hit control-S which applies the "edge sharpen" adjustment to a photo with the default values. You can even set it so the sharpening is applied to every photo at import, so it takes no time at all.
However, you may not necessarily want to do this: Sharpening is an "expensive" adjustment in terms of CPU usage so it will make other adjustments on a photo slightly slower. In general, I add sharpening to photos at the end of editing of them; and given I will be applying some adjustments to any photo that's going out of Aperture (i.e. I'm publishing it), I just hit control-S at the end of that to add an edge sharpen adjustment.
I'll also note the default edge sharpening values are a bit strong for my taste. They can make photos look a bit "crunchy." You can dial them back and save that as a default if you want.