Everybody follows that convention, from big commercial companies to small open-source stuff. Quite frankly, those who don't follow it are the ones who don't know how version numbers work.
Of course it isn't
wrong, as in getting shot for it...
But it is making things much more confusing for almost all people. And, like what happened in the past more than once already with scripts and plugins, people wont know what the latest version is because of this. That is if the next version would be named 1.2 again instead of 1.20....
Even the sole fact that for "1.1" you say "version one point one", and for "1.10" you say "one point ten" not "one point one".
So with the convention you described you still should call it 1.20 and not 1.2, just to avoid mistakes. Because with the convention you descibred it would be the same anyways. And although with the normal convention it isn't the same, it will avoid confusion as to what version is a follow up to the other.
So if the next version is called 1.20, the convention you described could still apply, if that is what he want to do... But it will also avoid confusion to those who (logically) assume the normal convention is used. If the next version is called 1.2 it will cause many people to not knowing what is what.
Anyways, He can jump from version 1.0 to version 12.345 for all I care, but whatever convention you use, you need to be consistant. Which is my main point actually... The string "1.10" is not the same string as "1.1" and in the comments it is stated this is "1.1" and when you import the script and in the script list it is stated as "1.10".... Both numbers must be the same at the least.
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