Q:

Language construct ~to by

What is the difference between the following two wrt their meaning for to by versus by:

An Internet standard is thoroughly a tested specification that is
  useful to and adhered to by those who work with the internet.

What if the group of words adhered to by those in the above sentence is replaced with adhered by those?
If doing this would bring any change in overall meaning of the sentence?

A:

Your alternate construction wouldn't work.
The simplest answer to this is that adhered to is a verb phrase in and of itself. You cannot drop the preposition.

I adhere to kosher dietary restrictions.
I adhere kosher dietary restrictions.

The first example is grammatically correct, and while the second sentence may be understood in meaning, it's wrong.
Other verbs don't require this structure:

I follow kosher dietary restrictions.

Follow works as a verb without a prepositional component. Other verbs may require these components some or all of the time in order to be grammatically correct. 
Adhere is almost never used without a preposition, but in the case of some of the other examples below, such as submit, certain usages do not require a preposition.

I adhere to...
I aspire to...
I abstain from...
I refrain from...
I comply with...
I interact with...
I conform with...
I defer to...
I submit to...

Going even further, you can link these verb phrases with other constructions:

I aspire to adhere to kosher dietary restrictions.
I aspire to follow kosher dietary restrictions.

As is the case with many languages, you'll have to rely on memory to determine which verbs require special constructions in order to make grammatical sense.

