I don't think online is "harder" than live play. I actually think the opposite...
You'll see more weak/bad play/players at higher stakes in live games because the "entry level" NLHE game in most card rooms is $100 buy in.
Internet players (even beginners) also have a little more "savvy" than their live counterparts. They own or have access to computers, have internet access, and have gone through the trouble of depositing or won money in
freerolls. They're also more likely to have been exposed to poker culture and are more apt to understand that there are some tactics/strategies are more profitable than others. In live games you get drunk people, w/ cash in their pockets, stumbling out of night clubs, saying "Hey, let's play that "new" Texas Hold'em game!" Guys buying their wives (who have never played poker) into 1/2 games so they can go sit 2/5.
Even though the opposition may be weaker, I actually find live play more difficult. Playing online, most of the important information is in your face. Pot totals, the amount of players in the hand, stack sizes, and bet amounts can be referenced at a glance. It takes some effort to keep track of all that in a live game. Especially when you're interpreting your opponents body language, having a conversation w/ the drunk guy, and trying to look like you're just there to have a good time.
It may be easier to be distracted playing online but it's easier to get "lost" playing live. The game is much slower, boredom hits quicker, and you find your eyes wondering up to ESPN or following that hot young cocktail waitress around the room. I think her name was Amber...