The idea of allowing source-control history to illustrate the "old way" of doing something rather than commenting it out and checking in the commenting-out along with an explanation is a good idea in theory.
In the real world, however, nobody ever looks at source control history on the files they are working on unless it is part of an official review process of some sort (done only periodically), or if something doesn't work, and the developer can't figure out why.
Even then, looking back more than about 3 versions basically never happens.
Partially, this is because source-control systems don't make this sort of casual review easy. Usually you have to check out an old version or diff against an old version, you just see two versions, and there's no good concise view of what changed that can give you an at-a-glance idea of what changed.
Partially, it is the combination of human nature and the needs of the team. If I have to fix something, and I can fix it in a few hours, I'm not likely to spend an hour investigating old versions of the code that haven't been "live" in a month (which, with each developer checking in often, means back many revisions), unless I happen to know that there's something in there (such as if I remember a discussion about changing something related to what I'm doing now).
If the code is deleted and checked back in, then, for all intents and purposes (except for the limited purpose of a complete roll-back) it ceases to exist. Yes, it is there for backup purposes, but without a person in the role of code librarian, it is going to get lost.
My source control tree on my current project is about 10 weeks old, on a team of only about 4 engineers, and there are about 200 committed change lists. I know that my team does not do as good of a job as it should of checking in as soon as there is something solid and ready to go. That makes it pretty rough to rely on reading the code history for every part of the code to catch every important change.
Right now, I'm working on a project in initial development mode, which is very different from a project in a maintenance mode. Many of the same tools are used in both environments, but the needs differ quite a bit. For example, often there is a task that requires two or more engineers to work somewhat closely together to build something (say a client and a server of some sort).
If I'm writing the server, I might write up the code for the draft interface that the client will use and check it in completely non-functional, so that the engineer writing the client can update. This is because we have the policy that says that the only way to send code from one engineer to another is through the source control system.
If the task is going to take long enough, it would be worth creating a branch perhaps for the two of us to work on (though that is against policy in my organization -- engineers and individual team leads don't have the necessary permissions on the source-control server). Ultimately, its a trade-off, which is why we try not to institute too many "always" or "never" policies.
I would probably respond to such a no-commented-code-ever policy by saying that it was a bit naive. Well-intentioned, perhaps, but ultimately unlikely to achieve its purpose.
Though seeing this post is going to make be go back through the code I checked in last week and remove the commented-out portion that was both never final (though it worked) and also never likely to be desired again.
