War Wizards of Cormyr (and even the prestige class) is another example of a faction of mages who expect martial training. They're a bit more real than Gandalf. Eldritch Knights, Spellswords, just some more PRCs where melee wizards were 'encouraged.' Like I mentioned, you don't have to be the best at something just to be able to do it. Its about playing a character, and if by chance, in the case of my own character, someone decided to teach you to use a sword and shield to defend yourself in the circumstances you might not always have a spellbook to protect you, It led to some rather indepth roleplay.
In terms of mechanics, a level 6 wizard is roughly the same as a level 3 fighter.. just slightly less HP and less armor.
When you look at things in a longer term.. A level 12 wizard is a level 6 fighter, but might have access to certain utility that can't be cast on the fighter. Globe of Invulnerability is the big suggestion, one of the -best- utility to have in some of more difficult places.
I shall just assume you've never dungeoned with me, or anyone else who knows how to pass off a rather decent melee-mage. (We are a few minority)
Would you like to ridicule me for taking Exotic Weapon, Light Armor, and Shield Proficiency as a wizard?