I went and had a look at the Park Tool website as well as a few others and I think I understand what was confusing me before and I believe that I know where I was mistaken in my original thinking. If I now understand correctly Giga X Pipe (GXP) BBs are a kind of external bearing system used by Truative and SRAM. There are other kinds of external bearing systems which different companies are using such as Shimano's Hollowtech II and Campagnolo's Ultra Torque. Each manufacture is making a slightly different external bearing system and using that exclusively. ( excluding BB30 )

Wikipedia is saying that the GXP BB is basically an evolved form of the older ISIS drive. The GXP has a longer spindle which has been pressed into the right crank and the bearings now sit outside the BB shell. One reoccurring complaint about the GXP BB seems to be seal drag but also that seems to be a problem which all the external bearing systems share. So I don't see that as a reason not to buy a GXP BB as much as it is a reason not to use EBS BB.

My questions would then be.
1. If I want to use a SRAM GXP crank sets am I forced to use a GXP BB? ( It would not be possible to use the SRAM GXP crankset with Shimano's Hollowtech II BB )
2. Is there any reason other than seal drag with the GXP BB that I should think twice about?

I will just add, that I have pretty much all but made up my mind that I will go with SRAM components mainly because I want to try something new after +70,000 km riding with the same components. Shimano has been great, I have no complaints but I want to see what else is out there and SRAM is actually the cheaper choice here. Right now cheaper does suit my budget better but really I just want something new to play around with and I can afford SRAM.