Actually, I'm pretty ***** confident that this is something that varies from bike to bike.
It's not a question of it being a "tight" fit -- in the case of my bike, on the front there is not only the "horn" on the tank, but also the bracket that the side panels mount to. On the rear, there's another bracket that the left side panel bolts to, and between these there is more than just a tight fit. Even after wiggling, pulling, prying and the incidental scraping away of some of the battery plastic on the front brackets, there was still no room to get the battery out. Remove the tank bolt and it takes about 10 seconds.
I am pretty much ready to strangle whoever was responsible for this particular feat of engineering. There's plenty of room to have moved the tray back a half centimeter or whatever. If you look at the side panels, their mounting holes are slotted, with just about the free play I'd have needed to get the battery out if the brackets had been attached just a bit more favorably. I assume there's manufacturing tolerance here, and if you're unlucky, there's no way to get the battery out with the onboard tool kit. To remove the tank bolt, you need an 8mm socket and a 10mm socket, and probably extensions to clear the frame/tank (a small open end or crescent wrench might work on the 8mm side).
Also, it's pretty annoying when people go on about how all you need to do is leave the battery on a tender or whatever and there's "no reason you should need to remove the battery more than once ever 4-5 years." Not all of us have a dedicated garage to keep our bikes in, amazingly enough, either because we're poor or because we live in an urban area.