You guys are reading the website/promo wrong. It says "Includes 1GB bonus", as in the details already reflect the additional 1GB bonus. What's double of 500mb? 1GB. Add another additional 1GB bonus = 2GB.
Otherwise you can also read the fine print.
8. 1 GB promotional bonus applies with a 2-yr term on in-market Individual wireless plans from $40/mo to $95/mo and $80/mo Family Data Share Plan. 1 GB promotional bonus included above and not eligible for Double minutes, texts and data bonus. Other offers cannot be combined.