Kathi is right, its the only difference.
If you don't have pets, I don't think you would need it. I will say that the pet head on the DC25 is much better than the first generation one which was total garbage.
Save yourself the $50.00 and skip the attachment. But if you do have pets who shed, get the attachment. Its now worth it.
The vacuum weighs 16lbs, which is not a light machine. Two things that make that okay, even good: 1) the vacuum is very maneuverable due to the ball design, so it's easy on the wrist and very nimble to turn. You don't feel the weight when you're pushing the vac around; 2) the weight of the vacuum means that you don't have to push down into the carpet in order to get good suction. I have had mine for around a year now and still like it a lot. The vacuum does what a good vac should do -- pulls up a surprising amount of dust from carpets.
My Dyson is simply the best vacuum cleaner ever made. I often have a Shiba Inu as a house guest and there are times that he sheds like a Porcupine dropping quills. I wouldn't be surprised that my Dyson sucked up house rats, cats and small children. I often loan it to friends and they are amazed what it pulls up from their rugs. Easy to clean and use. I would recommend a Dyson to everyone.
Hi Terry - Your question is exactly why I purchased this item. I had a different Dyson and it only had a bare floor and carpet setting; it wouldn't move forward at all. The "ball" is excellent - easy to maneuver and does an excellent job! Heck, even my stepson likes using it!! We have a very high pile/high desity carpet and no complaints. Hope this helps!