Actually, I think you've answered your own question. I've underlined the important parts. Three comments:
a) If you like flicking through pages and pages of backgrounded or suspended apps, that's your preference. Personally I like tidiness.
Then you just maintain a curated history of app usage as a quick launching service. Nothing against that, but it might be easier to put all the apps that you want to keep in the app history just onto the first two pages of the homescreen. To get to your 20 most used apps is much faster via the homescreen than via the app switcher.
b) Some apps don't reach the suspended state quickly. Instead they use a feature in IOS which allows them to request a 10 minute extension to their background status. If you inspect the running processes on a jailbroken phone, you will see that certain apps are really very badly behaved. They keep on using CPU and memory as long as 50 minutes after they cease being active. That's because they are repetitively requesting a 10 minute extension of their background status from IOS. IMHO, Apple has been way too lenient about this.
I would not worry about that 10 min limit but apps that misuse it like you describe it definitely deserve to be killed. But only those apps and not just all apps, killing all apps to catch a few bad apples is not a very efficient way of doing things.
c) As you've mentioned, certain type of apps will keep on running in the background (for valid reasons). However they do consume a lot of resources, which is something you seem to take entirely for granted. Many apps that track your movement (ski, bike, nav app.) can drain the battery of an aging iPhone 4 in less than 7 hours. To me it's obvious that when you take your skis off at lunch, you're going to want to kill that nice ski app. Ditto for other sports apps. That's why I like to keep my apps tidy as stated above. Otherwise I'd have all sorts of apps open.
Again, agreed. But that is just a few select apps. I kill those apps too but they are only a small fraction of the apps I mostly use.
Finally, I don't understand your need to question our motives. If we're closing the apps, it's not because it's 'useless' as you're trying to imply. It's because we've observed the effect certain apps have on the phone in real life. RR2 doesn't run well at all with those com and nav apps in the background. Why should I keep them there and have a degraded gaming experience?
If people create the impression that it is best to always kill all apps because they are misinformed, they misinform others. If your motives are based on misinformation and because of this you misinform others, one is perfectly justified to question your motives.
As for your purge question, no I never run it. Because it's not necessary.
There are situations where it can be beneficial. The clearest cut case is Handbrake. It uses a lot of memory and then releases it, creating a large pool of inactive memory. That is not bad in itself, but in the process of requesting and then releasing memory it pushes out all inactive memory used by other applications. This can lead to degraded performance in these other applications.
Of course, running purge throws out all inactive memory. But it takes a while for Handbrake to chew through all free memory again (depending on your processing power and total memory). During this time (ie, before it has gobbled up all free memory), being able to have other application re-use their own inactive memory can lead to a noticeable performance increase.