I've read all of the Showcases, and from memory, only one or two short stories from the last four years has actually not used post-modern techniques. Some use it more so than others, some use it more creatively than others, but ultimately, you've gotta do something visual in your short story if you're aiming for Showcase. This also applies to poetry, but I'm yet to see a post-modern script / screenplay or critical response (can you imagine?) in the Showcase.
I'm generally not into the whole post-modern thing, and I can say I honestly feel that a lot of the works that get into Showcase do not deserve to be there. Especially Showcase 2004 - if you want to learn how to bullshit a reflection statement, that's a good starting point, with arrogant lamers stating they "exceeded their expectations" of themselves and that their audiences should be "highly sophisticated and intelligent... intended for publication by a small, boutique publishing house like Duffy & Snellgrove". The story attached to that reflection statement was awful too, which makes me think that many good writers who choose not to use post-modern techniques will not get a 50 for that reason alone.
/rant
Sorry. But yeah, basically, if you're aiming for Showcase you've gotta do something visual and highly publishable.