This is patently false for one reason - once someone has a U.S. green card and has met the residency requirement to apply for citizenship, the application form and process are the same for everyone, regardless of how they got their green card (through work, marriage, asylum, investment, etc.).

Once you are eligible to apply, the whole process is basically form N400->biometrics->interview (just doublechecking your name and other paper info, takes 5 minutes)->civics test->ceremony.

However, the timelines and process for getting the green card itself is different depending on the nature of your visa, and they will indeed try to check for scam marriages before you get your green card (if you were applying for it through the marriage visa).

Not exactly, if you're married to a citizen the residence requirement is 3 years not 5, and the form clearly distinguishes the 3 and 5 year options (3 years requires extra evidence of marriage and spouse's US citizenship)

I stand corrected.