The 15th anniversary robe was desireable generally for a status symbol. (or had personal sentimental value to those who physically attended the event or won the contest)
you can still find one relatively easily, (because theres lots of them) if you still want this item as a status symbol. Obviously this wouldnt apply to personal sentimental value becuase that person would already have one.
you can get the commemorative robe for very cheap if your not concerned with the status symbol element, and just want to show your support of "commeorating" all the years of Ultima Online, plus have something a little special not available from in-game play.
To me, it just seems that those complaining about the new title never had motivations for actually wanting the 15th anniversary robe, but rather the status symbol associated with it but without the cost. The year is a non-issue. The Commemorative Robe, while more generalized, can be interpreted to Commemorate all, or any year in UOs long history.
Tho i was never a fan of these robes, or items that break the immersion of the game in general by association with Real Life dates / events, i think this move by the devs is a very appropiate one considering the history, reasons for desirability, and symbolic value of both versions of the robe.
I do agree it was a blunder on the devs part to accidentally release the 15th version for a very short time. yes a few people wil profit off this mistake. but its also not the first, or the last time that people will profit off of a mistake that was only there a few days. Think pre-patch imbued weapons. only available a few days, used to sell for over 1bil each. like the SC FC1 bokutos. But also, most collectors are aware that a few more hundred are out there, and price had already come way down on these robes. they were originally worth 800m, in the past year were down to 400m, and after the store item, similar graphic of Hawkwinds, and the initial mistake release are now only worth around 200 to 250. In short, theres not an overwelming gap between the 15th version, and the 5 dollar version. Its a gap yes, but not an astronomical one.
On a side note, Hawkwind's robe looks virtually the same and is available from normal, in-game play. and has useful mods.