I actually don't find the that useful to be honest. I work pretty close to my PC all the time and I get that the wires are a nuisance but I don't see the point of wireless mice and keyboard not unless you're really far away from the computer or you have a bizarre set up. And besides, wireless devices are pretty expensive and you still have to buy batteries or charge them.
That is exactly how I feel, I think that was a "trend" that appeared to be super modern a few years ago when the wireless fever came up, but it has just shown that it's not practical and it's more expensive, I feel more than 90% of the people keep using the wired versions.
Strange, I can't think of a time I WOULDN'T use a wireless keyboard or mouse for my desktop. I use the logitech wireless mouse and absolutely love the feel and response of it. I also play video games a lot online and it's been performed better for me in that area. As far as the battery thing goes, the Logitech takes 1 AA battery like every month. So you're buying a $3-4 12 pack of double AA batteries for your mouse a year. That shouldn't be too much of a financial stress for most people in what I consider a better product.
You are the first person that I know that uses wireless mouse and is happy with it. The way you put it in fact it's not such a big expense or trouble, just changing the battery once per month, but I am just happy with my wired mouse.