It's a hard decision. If they release everything at once, typical customer will buy one game and maybe come back later and buy another.
If I release a "new" game every week and all the gaming blogs run my press release, telling everyone what "new" game was released this week, then it increases the odds of me remembering "Oh, I wanted to buy that!".
Case in point. I have all of the DSiWare Game and Watch titles, along with the first Game and Watch VC title. The second would have been a day-one purchase for me, except that the thread about it went to s*** and I forgot about it being released... so I didn't buy it that day. It was several months later (not too long ago, in fact), I got linked back to that thread and remembered that I wanted to buy it.
Yeah, it's been there in the shop the entire time, but if no one talks about it, it hurts sales.