Is this intended to scan only vbscript? I assume that only Internet Explorer runs vbscript which is why I guess that Script Shield only applies to Internet explorer.
If my assumptions are correct, it will be a welcome addition to Avast! free.
No, it is ment to detect all kinds of malicious scripts not just vbscripts.
There has to be a difference between the free and paid versions of avast.
And this is one of them.
You cant have everything for free 
But you can have script shield. 
It’s included in the free version since the beta of v6.0
asyn
It’s good to see Script Shield in free versions
But now there’s not so much differences between free and paid.
Don’t worry, there will be new differences.
asyn