I have owned a DL-103D for almost 40 years. Prior to that I experiemented with a lot of MM and MI cartridges from ADC, Pickering, Stanton, Shure, Signet, AKG and others (I can't remember them all). Most of those cartridges were decent enough but each left me wanting for something that they didn't do.
To give you an idea about my preferences, I like planar or electorstatic transducers as opposed to boxed dynamic speakers. The dynamic speakers always sounded too slow to my ears and the boxiness of the enclosure drew too much attention to the speaker. I value very fast transducers that are neutral and transparent sounding.
The DL-103D made all the aforementioned cartridges sound closed in and congested. The 103D has also tracked everything I have tried. I have also owned a DL-300, DL-103, DL-103R and DL-103M.
The 103 was originally designed for use in the Japanese broadcasting industry and caught on as an unassuming plain jane cartridge that did a lot of things really well. Changing its cantilever and stylus raises the 103 and 103R's performance to heights that other, much more expensive, manufacturers make a big deal about. The Denon cartridge just does it with a design that is decades old.
Not only does the 103 and 103R sound very good in their stock form they sound good and don't give any trouble about tracking difficult passages. And they do all of the above for a very reasonable amount of money.
There are a lot of vinylphiles who own significant playback rigs and a number of these people choose to use a DL-103 or DL-103R (in stock or hotrodded form). I have read posts from 103 users that have owned much more exspensive cartridges and have settled on the 103 because it sounds good and works without a lot of fussy nonsense. The best cartridge in the world isn't very useful if you spend all of your time trying to get it to work properly.
In short the 103/103R is one of those cartridges that does so many thing well that its a hard act to follow up. There is no doubt that there are many cartridges that can outperform the lowly 103 but the 103 is musical, tracks well, gets your foot tapping and is inexpensive.
We have all fought fussy gear and had the pride of making it work when it worked. Denon cartridges all work very well and they sound much better than they should given their price. Thats a very hard thing to argue with, draws buyers and thats a good reason to keep manufacturing them.
I have no evidence to support ths, but I get the feeling that Denon would rather not be making the 103 and would prefer if the audiophile community would focus on its newer designs like the very good DL-S1. Denon is a major electronics manufacturer that still makes cartridges for a very small market. Its a wonder that they make cartridges at all. Any of them.
I'm certain that they are not in the cartridge market for the amount of money they make from that product line. Denon concerns itself with much larger market products and, as of this writing, cartridges are listed as accessories on their websites. These are products that are sort of stuffed in a corner. They make cartridges because they are still in the analog market and currently analog is enjoying a resurgence.
I often read posts from people who are having trouble with their playback rig. Things like inner groove distortion, mistracking and all manner of cartridge performance issues are listed in this and other forums. I have had none of these issues with my 103D (for almost 40 years), my 103R (when it is used as a backup), the 103M or the 103. Many people post about their delight with Denon cartridges both from a sonic standpoint and from a standpoint of their tracking ability.
I like Denon cartridges because they are very good, work every day, on all LPs and don't cost an arms and a leg. I admire boutique manufacturers of fine cartridges but Denon manages to make competitive products without having a cartridge wizard sealed in a secret dome with 25 9s wiring, with silver plating, hand assembling a cartridge that costs 10 of thousands of dollars. Of course that boutique cartridge must perform better. Or does it?