GorillaPod doesn't come with a ball head, but since its legs are extremely flexible will I actually "need" a ball head?
Can't I simply bend the legs to get the view? Am I missing a point?
To some degree you can adjust the legs or bend it so the camera faces where you want it.
But let's say you have it wrapped around a railing and want to aim the camera elsewhere. With a small ball head you can turn the camera easily. If you have to adjust the legs, it may take a lot of trial and error to position the camera just right.
Or if you have it on a tabletop, like a normal tripod, and have it balanced, but then want to point the camera up or down, again with a ball head that would be trivial, but if you have to bend legs to aim the camera the direction you want, you may unbalance the whole thing and once more it takes some trial and error to get it positioned.
If you're patient you can do without one. If you use it all the time you might get frustrated and a small ball head might be worth while.
No, but a ball head does offer real advantages
Using a gorillapod without a ball head is a practical option. As you point out, you can use the inherent flexibility of the tripod to angle the head in any direction.
However, if you add a ball head then you can point the camera in the right direction with much greater speed and accuracy. This may be crucial when shooting multiple images which will be stitched to gether to form a panorama, for example.
Also, as @MikeW points out, there are circumstances where the legs are wrapped round a support, so can't as readily be used to change angle.
As with so many things: it's a trade-off and it's your call.
I would recommend a ball head, it's very hard to do minute adjustments without the ball head. I was using a gorillapod without ball head, but later bought a ballhead. It's very easy make composition corrections with ballhead and also to go for portrait.
Joby sells a Gorillapod with ball head http://www.amazon.com/Joby-Gorillapod-SLR-Zoom-Flexible-Tripod/dp/B002FGTWOC
yes, yes and yes. I bought a gorillapod for my canon 550D and it was useless - I was spending more time adjusting it than taking pictures. if I'm honest, I had read reviews saying this before buying it, but I thought "it can't be that bad...otherwise they wouldn't sell any".
Actually, it was that bad! I've stopped using it. i didn't even try to buy the head, went straight to a more professional, full height tripod. looking back, the gorillapod was a nice concept (wrappable around objects etc) but completely useless.