In my vocabulary gross and sanitary are two different things. Sanitary is just
an objective idea about things being clean or not. Things can be dirty to some
amount. If something is unsanitary it says not directly something about the
significance of the effect on health and what it does with our experience.
Gross is unsanitary plus the impact it has on our perception. Even sanitary
conditions can be experienced as gross.
In my opinion pouring the way you first described is not very unsanitary but
instead mainly gross. It is because of that (consumer perception) why one
should not use the technique. There is little (no) prove that there is any
effect at all. But if one allows it for being a somewhat unsanitary practice
it can be easily relativated. It won't really significantly hurt people.
Compare it for instance with the effect of alcohol on public health and it
being a mayor cause of unnecessary death. The fun of alcohol is, without much
trouble, seen as enough credit to allow a high toll. Our minds has wicked ways
to twist the values in the comparison of different sorts of risks and profits.
Apparently we care more about the hardly relevant sanitary practices than the
dangers of alcohol causing a lot death. More:
http://www.google.com/#hl=en&q=death+causes+alcohol
Reasons for the pouring technique not being much relevant is because a drink
in a bar or restaurant isn't really a good habitat for pathogens and it is not
stored over long periods as well.
The number of pathogens possibly contaminating the food and entering (and
surviving) the body is very small. The human body also has a natural
resistance to these dangers when their magnitude is small. When eating a small
amount of cheese, for instance, one already can be almost sure to be consuming
some coliforms (the bacteria you'll find in faeces). If one doesn't consume
wrongly poured mixed drinks for sanitary reasons one shouldn't do a lot other
things as well.
When one tries to eliminate risks in the food chain one does not need to focus
on (a) every step but only on those which are relevant and (b) on single
actions for each risk. Health would be an unpractical concept otherwise.
Example (milk): (a) You'll pasteurise the raw milk (and the package) but not,
e.g. the glass from which it will be drunken. (b) after pasteurisation
everything is killed. You don't need to pasteurise again, e.g. just before
consumption.
In a bar this means that you could either focus on keeping gear clean, using
the gear properly or keeping hands clean. One also needs to focus on the
largest risks. Social hygiene (reducing alcohol abbuse, cutting people down),
risky ingredients (fresh products with reduced shelf live) and poisonous
ingredients (e.g. homemade products like bitters) are examples. More:
http://www.google.com/#hl=en&q=haccp
BTW, I believe that the second pouring technique (through a crack between
glass and tin) is not only less gross but also a faster method.