Google autofill & Roboform are form fillers, not entry services. Incidentally, autofill comes with the Google Tool Bar and it's not necessary to use Google Chrome to get it. I used autofill with Microsoft IE for years before I switched to Roboform
Entry services typicallly charge you a fee for which they'll enter you in sweepstakes. The sponsors and promoters of many sweepstakes aren't happy about this so they've started using captchas and rule restrictions to prevent it. Sweeps are a form of advertising. Where is the value to a sponsor if your entry is made by a third party and you never visit the Company website?
Here's a link for an explanation of Entry Serviices:
Can Automatic Sweepstakes Services Help Me Win More?
ps: You can Google "sweepstakes entry services" to find other explanations.