Most newer fluorescent bulbs require a ballast to run. Some fixtures just have it included in them. The screw-in CF bulbs require ballasts to work, but they are included in the bulb so you don't see it or need to buy it separately.
The bottom line is that looking at an AH Supply Kit, you can get the same amount of usable light into the tank with about half the wattage compared to screw-in CF bulbs. This is due to high-efficiency reflectors and bulb design/shape. I.e. if you had 40W worth of screw-in CF, you could accomplish effectively the same light level with about 20W of straight-bulb fluorescent with a high efficiency reflector.