A tube launched ASW torpedo has an even shorter range, but every ASW ship carries them. People get way too fixated on weapon range. Real warfare isn't like a game of Harpoon where he who has the longest ranged weapons wins.
An ASW ship needs at least one ASW helicopter and tube launched ASW torpedoes. If you add ASROC to that mix then you gain the extra capability of quick reaction.
Agreed that actual warfare is not a game. However there are some realities which are pretty inescapable with regards to ASW. The first is that in an engagement between a modern sub and surface ASW escort, unless the surface escort is receiving data from offboard assets, the sub will most likely be aware of the position of the surface vessel well before the ASW escort becomes aware of the sub. The second is that the weapons potentially available aboard a sub to engage a surface ASW escort with can well exceed the engagement envelope of the ASW escort's weapons which are capable of engaging the sub, if it were to be detected. What this in turn means is that a sub can set the terms of an engagement in it's favour and potentially take a position where it can attack the ASW escort from outside the max engagement range of the surface vessel, and possibly before the ASW escort even becomes aware that there is a sub in the area.
Now in modern warfare, the above scenario should not be allowed to happen, since other platforms like land and/or ship-based fixed-wing and helicopter ASW aircraft can be available which can extend the potential detection range of a hostile sub by tens if not a hundred or more km's beyond what a surface ASW escort can do on it's own. The USN developed a concept which described zones around "mission essential units" to provide a defence in depth against subs and other threats. The outer most zone is referred to as the surveillance area, and the likely assets active in covering this area would be MPA like the P-3 Orion or now P-8 Poseidon, as well as E-2 Hawkeye AWACS. The middle zone is referred to as the classification, identification and engagement area, and at present this area would primarily be covered by naval helicopters. The final zone, closest to the essential units, is referred to as the vital area and it is in this area that surface ASW escorts operate in, as well as naval helicopters. Now the size of the zones can differ depending on the maritime region and potential threat, but that last zone, the vital area is usually limited to the threat weapon range.
IMO what all the above means is that whenever and wherever possible, threats from hostile subs are to be detected and dealt with by ASW aircraft well before the sub can get close enough to be engaged by surface vessels. The two primary ASW roles for a surface escort in this concept are to provide a base to support naval helicopters and their crews, and to potentially deal with leakers if hostile subs manage to penetrate the first two zones, but even in the vital area, the surface ASW assets would be operating with and supporting ASW helicopters.
In such a scenario, where an embarked naval helicopter could potentially be operating 40+ km away from it's host or another ASW surface escort, then the capabilities of ASROC or VL-ASROC are moot. Also, expanding the potential threat scenario out, a ship, task force or navy might very well decide that there are better uses for the launch cell space that an ASROC or VL-ASROC might occupy. If the area the surface vessel will be operating in is within range of either land-based AShM, and/or land-based MPA or maritime strike aircraft, then I could easily see a threat matrix where having more air defence capability was called for, so thatan ASROC or VL-ASROC might get replaced by four ESSM, or an SM-2, or some other type or combination of air defence missiles.
IMO the USN does things a little differently because it can afford to, having both a greater quantity of assets than other nations, as well as those assets being generally more capable or having more potential loadout options. Four or eight VLS cells out of ~96, set aside for VL-ASROC would no IMO significantly degrade the available air defence capability of a vessel. That same four or eight VLS load out, when the total number of VLS cells is 32 to 48 cells is a bit of a different story.
