The problem is simple: if you give people just two options "landscape" and "street", than anything remotely "urban" is going to end up in the non-landscape option. People didn't get the intention of the rather specialised showcase category because the categories aren't sufficient as they say.
So, once the forum is cleaned up some time in the future, and the categories sorted out properly, we can probably solve this issue as well. Until that time perhaps rename this showcase section "urban" and be done with it.
I agree with your point about categories, especially about being too wide. That makes it difficult from two perspectives: that of the person who has an image he wants to post somewhere special; that of the reader who has interest in just one or two categories of photography, because he has to trawl through all sorts of stuff that may hold zero interest for him before finding his choice.
Of course, were it technically impossible for the site to handle that, it would just be one of those things, and folks would either sigh and trawl, or say to themselves - screw it, it's not worth the bother. However, as it's only some membership reluctance to observe any such kind of classification that makes life problematic, then the feeling is different, and people can easily get annoyed with that deliberate attitude.
There's no way of knowing, of course, but I wouldn't be at all surprised if relative disorganization has turned some casual viewers right off from joining.
Not for a moment imagine that the difficulty resides only within the unmade bed of street! Other image sections have been allowed to become totally confused, and as Russ suggested, might just as well be lumped together under a single all-things-to-all-men category.
(It's also alive and well on radio, where rock 'n' roll is repeatedly confused with stadium rock from the 70s, mostly another breed of beast altogether. You'd imagine a pro DJ would know that.)
So much potential thrown out with the neighbour's pesky cat.
:-)