The copy command is used to make a copy of a selection. If there is no active selection, the command shouldn't go and copy something all by itself, because there is no way for a user to understand beforehand what the copy command would do without an active selection.
Also, ctrl-c might be hit accidentally instead of hitting ctrl-v. If ctrl-c then clears the clipboard, you're punishing the user for this accident without any obvious gains (what use is an empty clipboard?).
Text-editors and IDE's however are very task specific and their users tend to spend many hours a day using them (for many, using a text-edtior pretty much makes up their working day). This allows users to learn hidden functionality by watching the application's behaviour. If there is even a small gain to be had by deviating from the normal behaviour, that might be warranted. Being able to copy or cut a line without having to make a selection is super handy when you're spending many hours a day shifting code.
A lot of software should be super easy to use for first-timers. Many people never get beyond that first-timer skill level. However, some software is inherently focused at power users. Power users need to be able to go further up the learning curve to become more efficient at using the software. Some software has an easy curve and doesn't break too many common patterns, so users can get an easy start. Other software, like Sublime Text, or more extremely Vim, hardly have any real first-time users. Their users will already be familiar with the basics and need to have tools at their disposal to become more efficient fast. With this head start and a motivated and experienced user base allows them to deviate from the defaults.
It's just another example where UX doesn't have a clear-cut answer that applies to all situations. Deviating from established standard patterns can actually be good UX even though UX-ers will spend a lot of their time fighting such deviations.