"I also notice an almost obsessive attempt to push water vapor off the table. Most global warming articles call CO2 as the most influential greenhouse gas after water vapor, but I can't remember the last time one of those articles showed by how much."

It seems that by defining a term, that literally they are "attempting to push water vapor off the table".

"global warming potential (GWP)
Definition

Ratio of the warming of atmosphere caused by one substance to that caused by a similar mass of carbon dioxide. For example, CFC-12 (a refrigerant) has a GWP of 8.5 (eight and a half time that of carbon dioxide), methane has 21, and water vapor has zero."
http://www.businessdictionary.com/definition/global-warming-potential-GWP.html

And:
"A GWP is not usually calculated for water vapor. Water vapour has a significant influence with regard to absorbing IR-radiation; however its concentration in the atmosphere mainly depends on air temperature. As there is no possibility to directly influence atmospheric water vapour concentration, the GWP-level for water vapour is not calculated; see greenhouse gas."
http://en.wikipedia.org/wiki/Global_warming_potential

This is not new, they have defined "forcing" to exclude water vapor also.

They concede that irrigation would regionally affect the amount of water vapor, but seem to be dismissive in regard this being significant.

Earth:
Land area: 148.94 million sq km
Land use: Arable land: 13.31%. Permanent crops: 4.71%. Other: 81.98% (2005 est.). Irrigated land: 2,770,980 sq km (1,721,886 sq mi).
http://www.infoplease.com/ipa/A0004373.html

So, 1.86 % of entire earth land surface [including arctic regions, ect] is farmland which is irrigated.

In the US: arable land: 18.01%
permanent crops: 0.21%
other: 81.78% (2005)

France: arable land: 33.46%
permanent crops: 2.03%
other: 64.51%

Iran:arable land: 9.78%
permanent crops: 1.29%

India: arable land: 48.83%
permanent crops: 2.8%

https://www.cia.gov/library/publications/the-world-factbook/fields/2097.html

So, in tropics temperate region where most of solar energy is reaching Earth there are significant areas which having water vapor added by human activity and *should* therefore fit definition of "forcing" or GWP but the higher beings have decreed this shall not be included.