The Main Roles of each class are:
each person has different opinions about it but one point certain is that World of Warcraft's graphic is good, but not the best
There is ten different classes/heroes, each is designed in its own way. You fight NPC's (non-player character, a computer) by using spells and hitting with a melee/ranged weapon. There is spellcasters and melee, they differ a lot. Melee has a higher amount of defense meanwhile the casters has less defense. If you would like to read more about the heros/classes of World of Warcraft, check out the WoWWiki site.
World of Warcraft has an Unlimited amount of gold. Each player determines his or her amount of gold by Questing, Selling, Farming, and Grinding.
World of Warcraft has three different plans for charging. Monthly, every three months, and every six months. Price total varies for each and is a negligible amount cheaper per month if you purchase it in three or six month increments.
There is only one World of Warcraft game. There are however, several patches for it, The Burning Crusade, Wrath of the Lich King, and Cataclysm. Which one is the best is very much up to each individual user as everyone has different tastes and opinions.
Around 25 gigs of memory is needed for all of World of Warcraft including each expansion pack.
This is better left to each person to decide. No-one can tell you which is better because they are two totally different games that have totally different play styles.
No, you must pay the $15.00 each and every month in order to play world of warcraft. If you don't pay you don't play.
No, the clients are programmed differently, because Apple and Microsoft computers operate from different code and are formatted completely different from each other.
They were different becuase each class did something different
No, you can not have more than one battlenet account on one licence of World of Warcraft. You can however, have more than one licence of World of Warcraft on each battlenet account.
The starter zone quests are different for each race. Each race has a starter zone tailored for their race, but this zone usually lasts only until around level 5. After that, they start sharing quests with other races of their faction.