Well, I'm not Deb, but since I'm in charge of the Front Page Showcase, I'll answer your question (and questions are always welcome here...)
I pick the articles to be showcased from a list of FW 500 (platinum) members. I try to pick from both Challenge Articles and Regular Submissions, and I try to pick a variety of genres--fiction, devotionals, poetry...
I used to pick through the list at random until I found something I liked, but then I became concerned that I might miss out on something wonderful that way. Also, my eyes seemed to be drawn toward names that were familiar to me, and I knew there were new writers out there whose work was worthy of recognition. So I started going through my list alphabetically (it's listed by first names, which is why October's showcased writers are all 'T' names).
However...a person is not guaranteed to be picked for the showcase, even if he or she is a platinum member. Some people join and rarely submit, or haven't submitted in years. Some people have very few submissions to choose from. And the showcased articles have to be very well-written, interesting to a broad audience, and nearly error-free.
Sometimes I'll just send the chosen writers a quick comment telling them that they've been selected. Occasionally, I'll find a piece that I'd love to showcase, but that contains a few glaring errors. If that's the case, I'll contact the writer and ask him or her to do a quick edit and re-submit the article before I'll feature it.
I hope that answers your questions...please let me know if there's anything else I can clarify for you!