This requirement applies to Authorized IRS e-file Providers participating in Online Filing of individual income tax returns that collect taxpayer information via the Internet. These Providers shall possess a valid and current Extended Validation Secure Socket Layer (SSL) certificate using SSL 3.0 / TLS 1.0 or later, and minimum 1024-bit RSA / 128-bit AES.
This passage refers to the service that may be offered by sites whereby you can file your taxes directly online from your own computer. The e-file program offers free filing to individual taxpayers with household income under a certain threshhold ($54,000 in 2007) and for-fee filing to any individual. (It also offers filing services to businesses and the self-employed, but those groups are outside this requirement, at least for 2009.) You may recall that online tax scams, including phishing attacks, have run rampant during the past two tax seasons. I believe that's what motivates this decision by the IRS, which seeks to offer e-filing to the populace in a widespread and egalitarian way while minimizing the individual's risk of identity theft.