Tom, Let me provide you with a real answer instead of a one liner...
BitCoin and LiteCoin run on two different types of encryption.
BitCoin runs on what is called SHA-256 encryption.
SHA-256 the first three characters (SHA) stand for "Secure Hash Algorithm", the last three characters (256) stands for the number of output bits (256 bits).
SHA-256 was "designed by the U.S. National Security Agency (NSA) and published in 2001 by the NIST as a U.S. Federal Information Processing Standard." (Wikipedia, SHA-2)
Litecoin runs on a lesser known, and much newer algorythm called scrypt.
"The scrypt function is specifically designed to hinder such [hacking] attempts by raising the resource demands of the algorithm. Specifically, the algorithm is designed to use a large amount of memory compared to other password-based KDFs, making the size and the cost of a hardware implementation much more expensive, and therefore limiting the amount of parallelism an attacker can use (for a given amount of financial resources)" (Wikipedia, scrypt)
After reading the description of the two algorithms we find out that scrypt is designed to be slow whereas SHA-256 is meant to be faster.
On a side note,
The creator of litecoin thought scrypt would impede large mining farms from controlling the network, allowing a more decentralized network. The creator also hoped to give equality to all users as they only had the ability to CPU mine at the beginning of litecoin's history. It was not until SolidCoin (referred in the bitcoin community as scamcoin) tried to compete with litecoin that a GPU based scrypt miner came out, Reaper. This emerging of Reaper was due to the main developer of solidcoin trying to discredit litecoin's abilities as an implementation of a decentralized currency.(Source. Myself, I lived through it). I believe that Reaper first came out in September of 2011.
https://en.wikipedia.org/wiki/SHA-2 (Retrieved 6/23/13@2345 EDT)
http://en.wikipedia.org/wiki/Scrypt (Retrieved 6/23/13@2345 EDT)
http://csrc.nist.gov/groups/ST/toolkit/secure_hashing.html#Approved%20Algorithms (Retrieved 6/23/13@2345 EDT)
as always, i may be wrong with information, if you do see errors, please let me know so i can fix it. Thanks!