There are multiple things going on in my head. The first is that depression is a symptom, and you treat the symptom of depression generally the same regardless of the cause. Someone with SAD can use the same medications as someone with Major Depressive Disorder, depression secondary to PTSD, etc. So, there are actually a lot of treatment options: all of the antidepressants (SSRIs, SNRIs, TCAs, MAOis, aminoketones...).
Another thing, though, is that Wellbutrin and Aplenzin are the only FDA approved treatments for SAD. That means very little to me, but may be important to the author/AN for legal reasons. I can't fault them for not wanting to run afoul of the FDA, since advertising medications for off-label purposes can get you fined. FDA approval is a legal and financial hurdle, though, and it's common to prescribe off label when the literature supports the use. Sertraline (Zoloft) is approved for the treatment of PTSD while escitalopram (Lexapro) and mirtazapine (Remeron) aren't, but that doesn't stop anyone from prescribing them if they seem appropriate.
Which brings to mind Sarafem, which is Prozac made into a purple pill and sold for premenstrual dysphoric disorder. They're even more closely related than Wellbutrin and Aplenzin - Sarafem and Prozac are the exact same drug. Sarafem is just a new name (Prozac has baggage), with a new effeminate color scheme to appeal to the market. So, I'm often leery of things like Aplenzin (a drug closely related to another drug that's now generic, marketed for a disorder that's new enough that most older drugs in the same class won't have FDA approval). But, that's my own baggage. :)