Starting from April 19, 2015, the requirements for a premium account as well as differences from limited (free) account has been changed. (Steam Limits Users Who Haven't Spent $5 to Prevent Spam, Phishing - GameSpot)

These changes are mostly intended for reducing spams, but it will also affect users who only buy retail versions or bundles outside of Steam.


New Premium account upgrade conditions:

• Buy games directly from the Steam store and spend at least $5 USD total (you now need $5 total to access Premium status, price didn't matter until this changes)
  
• Fund your Steam Wallet with at least $5 USD (this condition is unchanged)

You NO LONGER GET a premium account for:

• Activate a retail Steam game
  
• Redeem a Gift or Guest Pass
  
• Premium-only features

In addition to Sending friend invites, initiating chat sessions, and voting on games in Greenlight, the following features are now Premium only:

• Voting on Steam Reviews and Workshop items
  
• Participating in the Steam Market
  
• Posting frequently in the Steam Discussions
  
• Gaining Steam Profile Levels (Locked to level 0) and Trading Cards
  
• Submitting content on the Steam Workshop
  
• Posting in an item's Steam Workshop Discussions
  
• Accessing the Steam Web API