Wow, that document does show the process to be quite a labyrinthine... I would definitely support simplification of the process. I also think 5 years is too long (so long as the other requirements are met) and I think time spent legally resident with any kind of visa should count towards the threshold.
However, I do feel that people groups 1,2 & 3 are the only people any country should accept into its borders. Maybe with the addition of medium term visitors like students, people on prolonged business trips or investors.
5 years greencard-to-citizenship is nothing in comparison with how long it takes to get the greencard.
If you are a Filipino who in 1991 filed for family-based green card, because your brother was US citizen, then you are still waiting for your greencard approval. Yeap, 23 years later.
For anyone interested here are the requirements: http://www.uscis.gov/us-citizenship/citizenship-through-natu...
However, I do feel that people groups 1,2 & 3 are the only people any country should accept into its borders. Maybe with the addition of medium term visitors like students, people on prolonged business trips or investors.