Don't think their distribution systems could handle both games and apps being on sale at the same time.
I just hope they let you control what you see content wise, because I really disliked Newegg showing home appliances to me on their main page when I was there to look for deals on PC stuff. When before all I had to look at there was PC related stuff.
Like I know they let you control if DLC shows up on some of the lists and what not. So I think they can do it, I just hope they divide the store pages well enough to appease people who only want to see games or apps....and separate their sales on each to different times so you don't have to check various parts of their catalog for sales throughout the day/week.
Other than that, if they host some of the virus scanners/malware/etc stuff in their free versions at a minimum it could be useful. It'd certainly make it easier for people familiar with Steam to get these things to clean their own systems rather than hunting them down via browser searches. My brother picked up a virus that disabled his browsers, that was a new one to me.