As I said - there are two reasons behind this train of thought.
First, is not expelling the Gifts onto another object, and second, is showing respect to God over other people and things.
The first is obvious - don't spit, don't lick...etc. The zapyvka is to help you ensure that you have swallowed the Holy Gifts - but, there's no guarantee...so, you should still be careful.
There difference between sipping from a cup and kissing the icons - each hits on the different reason mentioned above.
The danger in sipping from the cup, I think you are stating that you fear that you might be leaving behind some of the Holy Gifts. This is why we should open wide...and NOT touch the spoon with our lips.
The danger from kissing the icons...in addition to transferring Holy Gifts via spittle....is that you are showing respect to the secondary, when you already have the primary within you.
This would be akin to walking past the bishop and asking the priest for a blessing.
The ONE thing that you should respect most, is within you at that very moment....unless you can work your lips around to give yourself a good kiss...there's little else worthy to be kissed right then and there.
To be on the safe side...when folks move in for a kiss of greeting after I've received Communion....all they get is my cheek....feel free to kiss me all you like!
I however, do not kiss them back.