Very few of Play.com's exclusives included bonus discs, I don't think Zavvi are doing anything differently in that respect. Catalogue releases usually exclude bonus discs, that is probably something beyond Zavvi's control.
I think that's the problem. Zavvi are trying to please everyone and they have certainly released a wide range of titles, something for every taste. The trouble is that many UK collectors are used to being able to buy all Steelbooks released and of course if you're one of those film fans who is willing to give any title a chance or have a broad taste, it becomes very expensive very quickly. I think the only thing we can do is try to prioritise wherever possible. Applying for another credit card would probably be a good idea too