Still, most Linux users expect to have their applications kept up to date. This is why they rely on the package management options that come with their distribution!
I can't stress enough just how fantastic ideas like Portable Linux Apps could be if there was an update ability to it. If this was in place, we'd see software installation as a cross-distribution standard that everyone could get behind!
No more running as root or touching the operating system like software installed through your existing package manager. The benefits are there, but these exciting ideas come at a price since you are completely reliant on a third-party for software updates. Worse, you'll need to visit the websites and download these updates manually. Speaking for myself, this isn't where I want to spend my time.
It should be mentioned that Debian and RPM packages don't self-update by themselves. So they share that in common with the alternatives listed above. However, if I install software with a Debian package, then later add a software repository offering Debian packages, that application will have the opportunity to be updated easily when I update the rest of my Linux distribution. This is why we see greater adoption with Debian and RPM packages than with any of the alternatives. They play well with updates.
Other distributions do have their own alternatives to Debian and RPM packages that work on a similar principle. In the end, the idea is that the ability to update the software should always be a viable option. This, not system resource concerns, is what I see holding back options like Portable Linux Apps from greater adoption.
If there was a way to enjoy the benefits of a Portable Linux Apps repository yet continue the distribution-agnostic benefits already offered, I could see standalone applications doing really well.
Let the users decide
Over the years there has been one constant that I've observed: Linux users will use what they want. And if what they want doesn't exist, they'll create it themselves. The greater takeaway here is that the Linux desktop is about choice. Therefore, the idea that one option is absolutely correct is simply absurd.
I know people personally who roll their own vanilla distributions and compile each and every one of the applications they want. Clearly, this is not the way I'd want to handle software management, but it works for those people.
Instead, I prefer anything using Debian packaging on my desktop. For me, it comes down to available software titles and the fact that, while imperfect, the package management that my favorite distribution provides works pretty darned well.