No, healthy sites should not have 30-50% search traffic. If that's what you have, you have too few regular users and are at high risk to lose a huge chunk of your traffic and consequently business at the next <random animal name> Google update.
Also, bear in mind that Google has acknowledged that keywords in URLs "help a little", so this is a good SEO win that has (arguably) nothing to do with how useful people find your content. It's much easier than putting effort into better content, too.
Actually the EMD update targeted EMD with low-quality backlinks to them. EMD that didn't have low-quality backlinks didn't seem to get hit. The goal of the update wasn't to penalize people with keywords in their domains.
Sure, you can still build a high quality site on an EMD, but the main reason for the update was because it was a spammer's paradise. The majority of people registering them were doing so with the intent of abusing the EMD's power at the time. In many cases, spam will get you to the top of the SERPs. But during EMD's heyday, spam + an EMD almost guaranteed a #1 ranking for the target keyword. People were selling EMD starter packages that would include EMD, 5 articles, and some link spam for good measure. It was fairly easy because of the weight EMDs were getting in the algorithm. I have no data to back this up. Purely my observations from being in the space during that time.
So yeah, I should have clarified a bit. I wasn't trying to imply EMDs were all penalized.
Actually your examples: mywhateverblog.com/red-widgets-in-texas/ and mywhateverblog.com/?p=545 isn't comparing keywords in URLs but Static vs. Dynamic URLS - and static URLs e.g. /red-widgets-in-texas/ is NOT better than /?p=545 - This is something that Google have even said so themselves[1]
I'm still comparing keywords in URLs vs. no keywords in URLs, but with no regard to static or dynamic.
To your point, I could have used static vs. static and dynamic vs. dynamic examples such as:
mywhateverblog.com/page1.html is not as good as mywhateverblog.com/red-widgets-in-texas.html
mywhateverblog.com/?p=595 is not as good as mywhateverblog.com/red-widgets-in-texas?id=595
From Google's own SEO Starter guide [1]:
"Use words in URLs! URLs with words that are relevant to your site's content and structure are friendlier for visitors navigating your site. Visitors remember them better and might be more willing to link to them.
Avoid using lengthy URLs with unnecessary parameters and session IDs; choosing generic page names like "page1.html"; using excessive keywords like"baseball-cards-baseball-cards-baseballcards.htm"
And from Google's Webmaster Tools page regarding URL structure [2]:
"A site's URL structure should be as simple as possible. Consider organizing your content so that URLs are constructed logically and in a manner that is most intelligible to humans (when possible, readable words rather than long ID numbers). For example, if you're searching for information about aviation, a URL like http://en.wikipedia.org/wiki/Aviation will help you decide whether to click that link. A URL like http://www.example.com/index.php?id_sezione=360&sid=3a5e..., is much less appealing to users."
Also, bear in mind that Google has acknowledged that keywords in URLs "help a little", so this is a good SEO win that has (arguably) nothing to do with how useful people find your content. It's much easier than putting effort into better content, too.