Shout Factory stated that they don't have any plans to produce full season DVD sets unless The Friendship Express sells a significant amount of copies in the United States. I don't remember the exact number, but it's very large, somewhere in the thousands. If enough US bronies purchase that DVD, the publisher may consider arranging season sets.
In regards to the iTune sales, nobody buys them, the amount of people who do is scarce. Those rips suffer from various issues, the most notable one being incorrect colors, the majority of bronies would rather download better TV rips from YouTube for free than have to pay for those same files just tweaked. In my personal opinion, I love owning physical copies of merchandise, you will always have them and don't have to worry about your harddrive getting nuked and losing everything. If the seasons ever get DVD or Blu-ray releases I will absolutely buy them.