I wish I could offer more explanation but as well as and does side by side sounds very awkward to me

This movie stinks as much as the other movie does

Noun + verb + comparison + Noun + verb

This movie stinks as much as does the other movie

Noun + Verb + comparison + verb + Noun

that was an awesome explanation!!!!.....

chidcguy,

I have seem some sentences with 'than do/does noun' usage and other with 'than + noun + do/does'.

There has to be a definite rule regarding when to use which usage.

The problem with (b) is the extra "a" in the sentence.

"just as well as does a commonly used and a more expensive drug" suggests that we're talking about two different drugs - one of which is commonly used and one of which is more expensive.

If (b) had read "just as well as does a commonly used and more expensive drug" it would have been great.

Thanks Stuart!

I must have read that sentence about 20 times and I did not notice that between option a) and b) there is an extra 'a'.

Now I can also see that option b) also fails s + v test - 'does' should be 'do'.