On my registry comment, I just wrote "It's a girl!" and left it at that. If you want to write more, you can say "Thank you for your love and support" and also like the suggestion above about the items not being set in stone and that your guests are free to get whatever they want and find appropriate.
As for registries, I try to remember when looking at them that just because an item is on the registry, it doesn't mean that the anyone is expected to purchase the item. Most stores offer discounts on registry items that are purchased by the people that created the registry. In that case, it makes sense to register for the big ticket items to take advantage of the discount (we registered for the stroller we were planning to buy, but had already gotten the furniture so none of that was on ours). Also, when I registered for my baby shower, the stores encouraged me to add items that I would need later, like baby proofing items, or toddler bed extentions. I didn't feel right about it, so didn't do it, but I can see where other people may just go with the store's suggestions not thinking about it (and again, for the future discounts).
Just do what feels right for you. If you don't need/want the item and don't feel comfortable having it on your registry, then don't do it. It sounds like you're being very thoughtful and that's a good thing!