The chance of solving 4 litecoin blocks is the same as solving 1 bitcoin block, sure.
But look at it this way. If bitcoin blocks were once a day, then if you had a few percent of the network power you would get 1 day = 1 confirmation ahead of your opponent all the time. But with bitcoin blocks every few minutes, you have an infinitessimal chance of getting 1 day = hundreds of confirmations ahead.
The distribution of timings is much wilder when you're only taking a couple samples. The longest confirmations in the world won't make 2-confirmation transactions completely safe, but 20 confirmations is pretty secure with any length.
But look at it this way. If bitcoin blocks were once a day, then if you had a few percent of the network power you would get 1 day = 1 confirmation ahead of your opponent all the time. But with bitcoin blocks every few minutes, you have an infinitessimal chance of getting 1 day = hundreds of confirmations ahead.
The distribution of timings is much wilder when you're only taking a couple samples. The longest confirmations in the world won't make 2-confirmation transactions completely safe, but 20 confirmations is pretty secure with any length.