The main difference between tournament hold'em and cash hold'em is that in tourney play, players get away with gambling more. Since there is a limited amount of time forcing everyone to play, the options each player has are limited too. Limited your options makes it easier actually, not harder. For example, if you have AT and a small stack of chips, you would go all-in in a tournament. You don't have this luxury in a cash game because most likely you'll be keeping a good amount of ammo on the table at times.

Another thing is that each decision in a tournament is based on a number of variables besides how the actual hand is sizing up your placement relative to the payout structure, your chip stack relative the blinds, busting a player out, giving a good player chips, etc, while in a cash game each hand is kind of an independent event. You might think that having all these extra things to think about makes things tougher, but it actually does the opposite. It kind of reigns you in and forces you to make plays that you wouldn't make in a cash game. An example of this might be going all-in preflop with a small pair. To do that in a tournament is commonplace but doing that in a cash game would be considered a bluff or just bad play.

Back to the time constraints, since the blinds are increasing, you are forced to gamble and play less than optimally. You might argue that it is an even playing ground since all entrants have to gamble like this, but anything can happen in the short term. Luck exists in the short term, not in the long term. Is tournament play just pure gambling? No, it's not, but even if you are a world class player, you can't expect to always win because you don't have enough time to really show your talent. See, if you challenged a pro basketball player to go one-on-one, he would dominate you everytime. In a poker tournament, you might actually beat the pro once or twice. If you keep playing him though, you would guarantee losing your shirt.

This is why tournament poker is feast or famine. The smallest percentage of poker players are those that make a living from tournaments only. Most pro players play in live games and tournaments.Cash games give a steady source of income and tournaments add some spice which can pay off big. The risk/reward is so generous in tournaments that you don't have to win often to do well. Next, how you do well in a tournament doesn't translate to doing well in a cash game (exp. Phil Hellmuth), but being a good cash game player translates perfectly into playing tournaments.