That is true. We should try this on Mars to see what happens, since we're not using it anyway... we won't know until we try. Gotta find us some
hostile aliens, or space elves and exterminate the hell out of them. For science.
Lol. Anyway, most of the 100-500kt range warheads were used in aircraft, submarine, SRBM or MIRV roles. For example, our Peacekeeper missiles could hold 12 300kt warheads or 1.2Mt MIRV warheads or a single, much larger warhead. We also use "dial-a-yield" which is a setting on the warhead that alters the yield by controlling the reaction. For example, a lot of aircraft based weapons used this, like the B83 (~5kt-1.2Mt), so you could select how much destruction you wanted to cause based on the tactical situation or just how genocidal you were feeling on that particular morning.
Likewise, the Soviets had/the Russians have the SS-18 which can drop 10 500kt MIRVs or one 20Mt-range single warhead. Mostly about target priority. Small military bases, carrier battlegroups, and smaller cities will get a MIRV, while big stuff or hardened stuff gets the big bombs. So NYC, Washington, Norfolk, San Diego, Moscow, St. Petersburgh, etc. will probably get a couple 20-meggers headed their way, while Albany or Tula might get a MIRV. MIRVs are also used for saturation bombing of a large target (Lots of little circles of death kill off more civilians than one big circle and use less U-235. It's a recession, shit ain't cheap) and getting through anti-ballistic missile systems, which nobody really has so that's kind of a moot point.
Of course, now they're trying to greenify the nuclear arsenal by turning perfectly good nuclear-tipped missiles into kinetic energy weapons. Basically giant bullets that fall down from space and make stuff not be there anymore with none of the nasty radioactive fallout, but still allowing you to destroy said area within 15 minutes of wanting to. Which is about as smart an idea as giving Bam Margera 2 kilos of blow and a case of hand grenades, due to the sheer unpredictability of how it may play out. For example, someday Urist McPresident may decide that he needs x building in Uriststan destroyed RIGHT THE FUCK NOW instead of waiting 12 hours for a B-2 to do the job (Yes, Virginia, we can bomb any target in the world from Missouri. Merry Christmas!), which sounds awesome until Comrade Urist McMissileCommader sees the thing and has literally no way of knowing whether it's just a big hunk of metal that's going to take out a random cosmetics factory or a MIRV bus ready to dump some buckets of instant sunshine on his kids. He then decides to err on the side of caution and end human life on Earth, or at least vindicate the message of the Fallout franchise.
Sorry, last part is a sore subject for me =p
Anyway, yeah, most of the warheads are in the sub-megaton range, but we still got a bunch of them big babies around for city-crackin' and the constant oh-my-God-I-just-shit-myself-when-I-thought-about-it-hard prospect of turning 90% or more of Earth's landmass into glass, ash, and cinders... leaving us a human race ruled by, and consisting entirely of, New Zealand. Still, gotta be ready for when those Chilean miners breach HFS...