It's a general point really, but it often occurs to me on reading these threads.
I do think that the process of watching a film is different from that of reading a book. Watching a film is generally a rather passive process - you can sit back and let the film wash over you - whereas reading requires much more active involvement. Perhaps, as a matter of psychology or biology I am wrong, but it just seems that way to me.
Because of this, I suspect that a good film-maker is unlikely to pay as much attention to internal consistency, practicality etc as a good author will. Slips are generally less noticable by film audiences (who - young children apart - generally only watch a film once or, if more, at infrequent intervals). That was particularly so before the advent of videos and, more recently, DVDs (and I can remeber a time before VCRs
). However, similar slips will be a lot more noticable in books, where increased concentration and interpretation is demanded of the reader, and the reader can also easily check back or pause to think things through. So film-makers are able to get way with a lot more. Added to that, in the context of films such as LotR, is the ability to explain it by reference to anything being possible in fantasy.
The reason I think this is that I have watched the films a lot less, I think, than many (possibly most) contributors to the Films forum and so never noticed most of the "slips" that have been brought up. I think I would have noticed much more had they been in the book, even on a first read.
Or may be I am just a much more passive (and easily satisified) viewer than everyone else...