This statement isn't necessarily true, the correct statement is that higher decentralized hashrate leads to a stronger network.
Here's a comment by coblee on that: https://bitcointalk.org/index.php?topic=165015.msg1723744#msg1723744
You can see some more info at https://litecoin.info/Comparison_between_Litecoin_and_Bitcoin#SHA256_mining_vs_scrypt_mining