"must obtain a Instrument Rating within 3 years or they have to resit their exams."
only if they wish to obtain their IFR rating. Keyword in the "IFR" enviroment is recency, and that includes exams that are not 10 years old !
"Is this true and if so how to general aviation pilots who operate VFR only fare under this ruling?"
It is true ! And VFR pilot just keep it that way....VFR !
"Does anyone know of anybody that has been affected by this?"
Yup, and they had to retake their ATPL exams to get their IR exam up to date ( since there wasn't anybody offering an IR exam only...go figure ).
Must be good, since people are willing to do it twice ( or they didn't look a the experation date on their exampapers!!!!!)