For WEP this is true, for WPA/WPA2 without WPS it is much harder. WPA2 uses PBKDF2 with 4096 iterations of HMAC-SHA1, this is a rather slow algorithm.
On (http://hashcat.net/oclhashcat-plus/) you can find some values on how slow it is. The same computer can crack 7 billion md5 hash per seconds, but it can barely do 181 thousand WPA2 password per second.
At this speed you would need more than 200 days just to crack a 7 letter password only using a-zA-Z0-9. And more than 38 years to crack an 8 letter password. If your password is a word or derivation of a word, you can obviously get it much faster with a dictionary attack.
