The Open Game License is a wonderful and powerful thing. The OGL came about in 2000 and was published by Wizards of the Coast to facilitate the spread of ideas and third support for Dungeons & Dragons (3rd Edition) with the use of an SRD they made available. It's been about 12 years now and the hobby has already seen the d20 boom and near collapse. Many small publishers have come and gone having put out various products to run with 3rd Ed. Others have chosen to use the OGL and SRD to create their own game or re-create others that have once been published. Castles & Crusades was one of these and there were many others to follow.
Recently, there have been a call to try and do another SRD for C&C. In principal, I don't think there is anything wrong with that. Unfortunately, I think there is a lack of understanding on the OGL as well as the spirit for which it was intended.
A good OGL will actually tell you what you can use as Open Game Content -- meaning that this material can be used in other products 'as-written', as needed provided that proper care is taken to cite the source and include it with the OGL which needs to accompany whatever you are using it for. A good OGL will tell you what you can't use, or at least provide guidelines. Some of the best examples can be found with various d20 products from Necromancer Games.
However, while permitted to do so, I'm sure that WOTC never anticipated Mongoose just take the text of the SRD and throw it together in a Pocket Player's Handbook to use as a substitute for their own PHB. Frankly, that's just bad form even if it's perfectly legal.
Why does this happen? Well, I suppose in some cases, it's as simple as a small publisher or individual who want to release stuff under the OGL that doesn't necessarily understand the whole thing or, maybe it's a simple mistake or omission of an important piece of information within the OGL. In other cases, it's also simple assumptions from fans wanting to use the material. They see OGL and think Open Game Content!
I had a good look at what was Open Game Content and what was not in the C&C PHB. It's quite nicely detailed and there is a lot of it. One of the things which is *NOT* listed as OGC is the 'Attributes & The Game' which detail the use of the Siege Mechanic. The Siege Engine is also listed as product IP. It's one of the very few things that is 'closed'. TLG has chosen to be very liberal with what they are allowing to be kept open.
But does this mean an SRD should include all the text, word for word from the PHB because it's declared OGC? Well, legally yeah. But I really think it's bad form if you do but that is just *my* opinion.
A few months ago, this sort of thing happened and a well intentioned fan did just that. There was something of an uproar from certain fans and ultimately, it was taken down. I'm not going to dwell on what should have been done or shouldn't. My understanding is that it was amicable enough and that's fine with me. But my understanding is that it was perfectly legal.
I just don't know if it was in the exact spirit of the OGL. That said, with the renewed discussion about a possible C&C SRD, it's only a matter of time before one surfaces and I think this is a very good thing.