I've put a lot of thought into this sort of thing. And here are the things I've decided that I believe.
1) The giver has absolute authority and right over the choice of gift. Period. And if you don't want to give something that's been requested or suggested, you do not need to. Period. No matter what the reason.
You don't have to have a "good" reason (like, an ethical one over a simple annoyance one). You are picking the gift.
2) It's not that cool, actually, to buy a similar-but-not-quite-the-same gift unless you're pretty sure that the person isn't that picky (example of proof I'd accept: on Elfster, I put a link to a couple of different guitar tuners and a note that says, "I need one of these, but I don't know which one; as long as it can do X, I'm happy"). Or if you're pretty sure they're really, really comparable (example: Lands End canvas totes are much like LLBean's).
The reason is because most people won't think they can get rid of an "almost right" item if they've already got it, and they feel obligated to keep gifts.
3) It's rude to give only one suggestion on a wish list.
(I actually think it's not that cool to put a gift card on there, unless you are saying something like, "I want to buy X big thing, and this gift card would help"; maybe it's OK if you say, "this store always has clothes that fit me." But a gift card on its own hits me wrong as a wish-list suggestion. And if someone asks you directly for ideas--for yourself or for someone else, saying "a gift card" is not cool. If someone were willing to give a gift card, they wouldn't be asking for ideas.)
And I totally agree with m2kbug:
My own opinion is lists are suggestions, not necessarily something you have to stick to 100%. It definately gives you ideas to work with and is very useful when you don't know about specific things they like music or scents or in the case of my son, which video games he wants. Unless the secret Santa rules are specific that you have to buy something on the list, I think it would be perfectly fine to buy something off the list he thinks the person would like based on the ideas from that list. It's probably safer to go with what is on the list if specific brands are listed or a specific color or style.
(Total grammar-geek aside--not a criticism at all, though: I get frustrated with the phrase "off the list"--it's like "biweekly": Does it mean "from the list" or "away from the list"? Because it could mean either. The English language is sometimes really, really annoying.)