ORIGINAL: simast
Alfred hit on several reasons why bombs can be preferable to torpedoes, but what exactly are you referring to when you say "turn to bombs"? If you can give a specific example from the spreadsheet, I can give you a better answer.
Hmm, I guess KB is good example - 4 out of 6 Kate groups are set to use bombs. Or there is Toko Ku T-1 Det flying naval search with bombs from Kompong Track with Air HQ and torpedoes available on site. (Are torpedoes used with naval search missions by the way?)
In my game the turn after setup - KB engaged a small force of CA and DMS ships - there were 7+ hits with 250 kg bombs on the CA but I somehow doubt it will go down from bombs alone.
And another torpedo related question - when the manual mentions that torpedoes can be supplied from Air HQs based on their command range. If you have Air HQ with command range 1 - does that mean it can provide torpedoes only to air units in the same hex or the same hex and +1 hex away?
I took a look at the spreadsheet and there are 17 instances in which the "Comments" cell includes the words "Using Bombs". The reason why can be different, so I'll address the major categories:
1) CV Air: As you noticed, 4 of the 6 Kate units in KB were switched from Torpedoes to bombs, and that is largely because carriers have a very limited number of Torpedo sorties available. Following the attack on PH, the KB torpedo inventory is severely reduced for four of the carriers (Akagi & Kaga are down to 18 of 43 while Hiryu & Soryu are at 18 of 36). Only Zuikaku and Shokaku have the full sortie load available (45 of 45). So the idea is to keep your options open, rather than risk expending every torpedo in 4 of the 6 carriers on Day2.
2) Naval Search: The Mavis and Betty/Nell can deploy either torpedoes or bombs, and personally I prefer that long range search planes have bombs for dropping on targets of opportunity (the attacks which only show up as a "ship spotted and attacked" message). Maybe that still happens if they are armed with torpedoes, but that also might make them more susceptible to AA. Possibly also gives them a chance to drop a bomb on a spotted submarine, whereas torpedoes *probably* won't work on that type of target.
That's the majority of cases, although there's a few one-offs involving training or transfer to a non-torpedo sortie CVE.
As to the Command radius, it is defined as "same hex plus radius number". So in your example, it includes the ring of hexes surrounding the HQ. You can see this in action by looking at the torpedo ability of the Nells & Betties on Roi-Namur if you add torpedo sorties to the HQ on Kwajalein.