The bombs in Fallout come from planes, not ICBMs.
No game ever told us that the bombs were dropped and instead they do say stuff that supports the use of or outright mention ICBMs.
Fallout 3 mentions a nuke being on a plane to explain Megaton, but it was never said (even in that game) that the nukes were dropped by plane. Even Megaton's crater was created by the crash of the USA's plane that was carrying that atomic bomb, not dropping the bomb.
Even Fallout 3 mentions the use of ICBMs:
-It mentions how the USA converted the Delta IX rockets into ICBMs. We can even find one crashed outside the Statesman Hotel (so we know that at least some were launched).
-Mothership Zeta, (in a captive log) mentions how the USA had more than 30 ICBMs on alert and ready to be launched.
-There are two instances of USA Orbital Nuclear Missile Platform use in Fallout 3, the "Highwater-Trousers" and the "Bradley-Hercules".
-In Fort Constantine, we can read the transcript of the automated launch system and it specifically states "ICBM RESPONSE/NUCLEAR":
|======================|
|MINUTEMAN XI - CONSTANTINE|
|LAUNCH PROTOCOL 10.77 |
|SECURITY CLEARANCE ALPHA |
|======================|
|EAM CLEARANCE: G 5 S S 1 8|
|* * >> USAF DEFCON |
|* * >> EXEC:'BAGMAN' |
|======================|
|AUTH CODE: 0000000000 |
|======================|
|RESPONSE SCENARIO MX-CN91 |
|ICBM RESPONSE/NUCLEAR |
|BASE COMMAND EYES ONLY |
|======================|
Fallout 2 intro mentions "Spears of nuclear fire rained from the skies.". Missiles are shaped like spears, bombs not so much.
In Fallout New Vegas we can see the USA's ICBMs (in Lonesome Road), Mr House describes his defence grid built for the purpose of saving Las Vegas as a "missile defense grid":
My networked mainframes were able to predict and force-transmit disarm code subsets to 59 warheads, neutralizing them before impact.
Laser cannons mounted on the roof of the Lucky 38 destroyed another 9 warheads. The rest got through, though none hit the city itself.
(...)
The Chip contained vital software upgrades, but not just for my Securitrons. Every aspect of the missile defense grid would have been upgraded, too.
Raul specifically mentions missiles:
I was in Mexico City when the bombs dropped. Even from there, we could see House's defensive rockets shooting down the incoming missiles.
In Fallout 4 we have a US Air Force base tasked with turning obsolete Mark 28 bombs into ICBMs.
Also in FO4, Captain Zao mentions that orders were issued to launch all of the submarine's nuclear missiles, which implies that all Chinese submarines got those orders too:
200 years ago, I launched all of Yangtze's high-yield nuclear missiles. As ordered. For 200 years, I have lived with that guilt. That shame. So much fire. Such bei.
In Fallout 76 the nukes are all ICBMs, and we can even launch them ourselves.
And there are probably more examples I can't remember off the top of my head anymore.