The original poster in both the title and the post asked why $1,200 slot wins are taxable and table wins of that amount were not. This is untrue. They both are taxable as winnings.
It then morphed into reportable. Once again ALL winnings are reportable according to the IRS by the individual on their tax return.
This then morphed into what triggers a W-2G. Grasp accurately answered what triggers a W2-G by a casino.
Once again, all gambling winnings are taxable and all are reportable. If one does not receive a W-2G and chooses not to report their winnings, or receives a W-2G and only reports that, that is up to them.
https://www.irs.gov/newsroom/article/0,,id=108277,00.html