If naturalized before July 1, 1912
Re: If naturalized before July 1, 1912
Also a fairly new requirement is a "Letter of Invitation". This has to be signed by an Italian citizen living in Italy. It cannot come from a non-Italian resident. Before my sig other was issued his Italian passport, he looked into the ER visa through the San Francisco Consulate. Apparently these requirements were added in 2007 as part of new EU security package. By the way, anyone who is not retired would most likely need to do some type of work in Italy and this is also not allowed with the ER visa.
Re: If naturalized before July 1, 1912
As with everything else, requirements vary by consulate. 
Retirees are not the only people with the means to support themselves without working. There are people who obtain ER visas (based on their investments and income) who do NOT work in Italy and they are not officially retirees. I know of several. You are right though, (unless things have changed), working in Italy is not allowed with this type of visa. That is precisely why the consulate evaluates an applicants whole financial portfolio when deciding whether or not an individual will be granted the visa. Might be foolish to apply for an ER visa knowing that you need to work to support yourself when you aren't legally allowed to in the first place.
Retirees are not the only people with the means to support themselves without working. There are people who obtain ER visas (based on their investments and income) who do NOT work in Italy and they are not officially retirees. I know of several. You are right though, (unless things have changed), working in Italy is not allowed with this type of visa. That is precisely why the consulate evaluates an applicants whole financial portfolio when deciding whether or not an individual will be granted the visa. Might be foolish to apply for an ER visa knowing that you need to work to support yourself when you aren't legally allowed to in the first place.