In Ruger's line, the only .38 Special-only gun currently cataloged is the LCR. While the LCR is available in .357 Magnum, the .38 Special version is both roughly 10% lighter and, more importantly, substantially less expensive (MSRP is $90 less for the .38-only version). Of all Ruger's other DA revolvers, which all have steel frames, no .38 Special-only version is cataloged.
I'm surprised no one caught this...
The SP101 is still made in .38spl with a 2.25" barrel (model 5737). While it is true that the GP100 is no longer made in .38spl, it was until fairly recently, and the SP101 certainly is still made.
As for the OP's argument (and continued argument despite all everyone had to say), of course there is good reason to continue making (and buying) .38spl chambered revolvers.
Sure, if you only plan to own one revolver, you'll likely shoot magnum rounds on occasion, and you want a medium frame revolver, you are better off buying a .357mag because it is a little more versatile. For the rest of us (how many at TFL only have one revolver), there are plenty of good reasons for .38spl chambered guns.
Like many have said...
.38 revolvers are usually less expensive than the corresponding magnum. If you won't really shoot magnum much, or at all, why spend the extra money? It simply makes no sense.
.38spl revolvers are usually lighter (when not comparing apples to oranges). This isn't just true with small J-frames. The S&W K-frames in .38 tend to be a couple ounces lighter than the same size magnum, and they are small enough to consider carrying (so the weight makes a difference).
Carbon build up. Shoot a lot of magnums and you will get carbon build up. Regular cleaning may not be enough, you may need to get special cleaners for carbon, or use methods like some have described here that are more intensive. You may not let it get to where it makes it hard to chamber a magnum cartridge, but it does mean extra cleaning and an extra step if you shoot .38spl out of a .357mag revolver.
Many people seem to think that .38spl is more accurate out of a dedicated .38spl. The idea is that the extra distance the bullet is traveling before hitting the rifling will harm accuracy. I haven't seen the idea tested. Even if one or two people did with their personal revolvers, it would be hard to come to a definitive conclusion due to possible variances revolver to revolver. It would need to involve quite a few guns to really be conclusive. However, it makes some sense, and true or not, it is a commonly held belief. If true, it certainly would be a good argument for dedicated .38spl revolvers.
Rules. There are still some security companies and correctional departments that issue revolvers. There are more (and some police departments) that allow them. Many that do allow them, do not allow magnum revolvers. While it may be the weakest argument for a dedicated .38, if an individual happens to fall under regulations that limit them to non-magnum revolvers, that's a great argument for that person to get a dedicated .38spl.
If you want a small frame revolver, especially a lightweight, .38 is often the way to go. For most people, .357mag is too much even in a steel framed small frame revolver, and definitely in a lightweight. Sure, some may be able to shoot it, some may not even mind the recoil that much. However, the excessive recoil in such a small and light gun means much slower follow up shots. If you are going to shoot mainly (or only) .38 anyway, the drawbacks of the .357mag chambering are good reason to go .38 only. For the steel guns, the price may be similar (at least if you are buying Taurus), but they will be much heavier. If you are buying Taurus, you no longer have a 5-shot .38 v. a 5-shot .357mag as your choice, they now have the 5-shot magnum and 6-shot .38spl in almost the same size (I would rather have the extra round of controllable .38 than the more power, but slower follow up shots, through the magnums). In a lightweight gun, the materials and manufacturing processes to allow it to shoot magnums is going to make the gun significantly more expensive. Sure, a scandium .357 will be a little lighter than the aluminum 442/642, but the 15oz 442/642 is as light as I ever want to shoot when shooting .38spl defensive rounds.
If you are in any way a collector, some seriously classic guns were made in .38spl. If you want a model 10, it will be a .38. If you want a Colt Police Positive Special, it will be a .38 (or .32). Even new production, I wouldn't mind a new S&W M10 just because it has a heritage that goes back to the original model 10s and prior to that the Military and Police revolvers.
If you own several guns, given that .38 may be more accurate, and certainly given some of the historical significance some designs have, why not have dedicated .38 revolvers
and .357mag revolvers.
Apparently none of them even want to consider shooting .357 out of a 12 ounce revolver.