This will probably get asked or pointed out, but there's a Apple iBook FAQ at:
and for right now, at least, you can only buy an iBook if you're on a limited set of Apple platforms:
Can I purchase a book from the iBookstore using my computer?
No, the iBookstore is only available through iBooks on iPad, iPhone, and iPod touch at this time.
You can view it on up to 5 computers, etc., the FAQ is useful.
But yes, if I don't buy an iPad, for now at least, I'd be blocked from the iBookstore. Not a big factor in my deliberations, but I suppose it might be for others. What is a factor is if I can Read the book from multiple providers (Amazon, B&N, etc.)