Once again, I would like to object to this policy, for several reasons:
Firstly, I believe the measure is counter-productive. On a busy wiki, it is never possible to have staff members present at all times. Normal users form an important part of the RC patrol who watch for vandalism. Why purposely reduce your vandal watch force by limiting their abilities? Reverting vandalism and warning the user is constructive in regard to the wiki, and shouldn't be limited. I also question the wisdom of this policy of always running to the staff members for help: shouldn't we try to become self-sufficient (and more effective) in dealing with vandals?
Secondly, remember that a warning is simply that: a warning. It doesn't necessarily lead to a ban. Sometimes a user will be banned without warnings. There is no "count" for the warnings, and thus no need to restrict the use or "meaning" to the template.
Thirdly, I would like to remind everyone that administrators - and by extension, all staff members - are simply normal users with the tools of ban and delete. Their opinions should not have any more weight in debates of policy or the mainspace, nor, in this case, in giving vandals warnings. They are trusted users, yes, but this trust should be because of their actions, not their position. An administrator may have the power to ban a user, but any user with a knowledge of the rules of the wiki should be able to warn a vandal.
Indeed, what would be the difference between me warning a vandal for three acts of purposeful page blanking, as compared to an administrator? The fact remains that that user vandalised, and thus should be banned. If we both left similar messages, the warning should have the exact same effect.
The maintenance templates as a whole exist to provide a consistent, unified set of templates which all users could use to flag issues. Having a mix of official templates and prose warnings for the same purpose (here I differentiate between a friendly heads up and a warning for vandalism) makes little sense in this context.
Finally, I repeat my message from previous forums, which I feel should be stressed more here: assume good faith. On the many wikis I've been to before, the userbase was trusted as a whole to use the warnings with discretion. If the problem is unprofessional warnings and multiple warnings for the same infringement, the solution should not be to revoke everyone's powers, but, instead, to educate people on how to use the wiki properly.