12ps dependent origination question: why phassa is meeting of three, not just "when eye contacts visible object, eye-consciousness arises"

Question

There is this line:
"Dependent on the eye and forms, eye-consciousness arises; the meeting of the three is contact."
Why did the Buddha describe this process in this way? Why didn't he say "When there is contact between eye and form, eye-consciousness arises"? Is there any subtle difference?
I do understand that the eye must be capable of seeing (e.g. not blindfolded) for it to see forms.

Answer

Because an internal sense faculty contacting an external  sense object doesn't mean a moment of sense-consciousness will definitely arise.

Even very ordinary scenarios, say a mosquito bites you at the same moment you see something and hear a sound, you don't necessarily register all 3 sense base consciousness.

Maybe just the ear consciousness registered with ear contact, and you didn't notice the sight of a road sign you were looking for. 

Similar question about requisite conditions

The question is also similar to a common one with 12ps, it seems to say if there is vedana, then tanha (craving) will arise. 

The thing we have to remember about the suttas, it's an oral tradition, and often the formulas memorized are very terse outlines, or part of a matrix, not meant to be interpreted with strict logic or grammar rules. There are often implied assumptions we have to incorporate, extra information not in the bare sutta words.

What the 12ps formula says, is that for craving to arise, 

there must have been vedana that arose previously for the craving to be based on.

Vedana is a requisite condition for tanha to arise.

It doesn't mean that if there is vedana, then tanha will definitely arise right after.

Or if there is tanha, that upadana will definitely arise right after.