Yeah, it's all explained. Despite of that anyway I do concur with you that's not ideal (the ratings), because it's a know fact among experts and manufacturers. Being a general advise for MnO2 tantalum caps it sounds more reasonable to change these caps ratings. I mean, no deal if something is rated based on the theoretical specifications but these same specifications doesn't apply to real world (as you pointed, a 100% difference from the recommended). It would help preventing mistakes like what happened in the shield. Well I'm not sure if it was a mistake or what because I'm just new to this information and maybe there are more details to consider to really tag it as a error in the design.
Anyway it was the second report I heard about this one cap catching fire (and it blew for ddewaele). People are commonly much near the boards while prototyping, despite not the recommended way of doing it, such event can hurt someone's eyes or bring fire on unattended experiments, what can be dangerous. I hope Arduino team fix this on future boards and issue a warning at the official shield page about the issue (if its really the case and it can be confirmed).