Can Audition do automation beyond drawing automation envelopes?
Yes. 2.0 added automation that functions as it should. 3.0 improves by adding a few features to it. Proper automation had been a major feature request prior to 2.0 and Adobe delivered a pretty typical automation engine. 3.0 adds some automation options not found in all DAWs. 12 years ago, the original Cool Edit was a shareware editor. Cool Edit Pro added a decent multitrack. CEP 2.0 incorporated real-time effects. Audition 2.0 added ASIO and automation, but had many flaws in other areas. 3.0 is finally equal to other DAWs in the multitrack environment, while remaining the most powerful
editor on the market. It has taken awhile to get there, but Audition has grown up. Pro Tools was always designed as a professional product. Cool Edit was a crappy editor with a crappy name. That means a lot of people won't take it seriously. It did, afterall, start as SHAREWARE!

But the other way to look at that, is that Pro Tools doesn't change a huge amount, from one version to the next. Audition grows hugely with each release and is NOTHING like the program that started it.
I've never heard of this. I own 5 ProTools rigs, both LE and TDM. The playback engine works fine on both systems, it sums, and behaves just like analog consoles do. Nothing I've read has convinced me it's worth taking the time to mix "outside the box" for radio promos. Can you provide a link to elaborate how ProTools mixing engine doesn't "automatically sum"?
Well, I didn't find anything concrete enough to post, following a quick Google search. There's a lot of talk about it on forums, but I couldn't find anything scientific or anything that would qualify for more than babble. But there's an easy way to check this for yourself. Just pay attention to the difference in sound between a mix and a bounce. You'll notice that they don't sound quite the same. Bouncing sums properly, whereas the mix environment does not. So you end up with a little different sound. I can't specifically say that one sounds worse than the other, but they don't "gel" the same, which is BS if you've spent a huge amount of time crafting a mix. Of course, there are sums taking place in the mix, but they are incorrect. It's certainly not a major sound difference, but it's there and it's audible. Though a lot of pros sum externally, it isn't needed. There are plenty of summing plug-ins. The Waves L3 is a good example of a plug-in that was designed to compensate for this oversight. Waves describes it as: "The world’s first auto-summing multi-band limiter..." I'm not aware of any other platforms that would benefit from an "auto-summing" plug-in. A lot of people blame the "plastic" PT sound on this, but I'm a little more fair and blame that on overuse/misuse/abuse of plug-ins.
I think PT is going to start taking some hits. Nuendo is catching on big in the pro market, and there are lots of great home options. I really think that if Adobe markets this well, they can grab a nice chunk of the home market. More than PT, however, Sonar looks to take a big hit. PT has to worry more about Nuendo, I think.
BTW, even though I speak poorly of Pro Tools, if Audition dropped off the face of the earth, PT would likely be my second choice. If Wavelab got a little more user friendly, I might go that route too...
Emmett