[binarybits]

I see what you mean. Three thoughts on this:

* The time lock on commitment transactions is typically set to be a few days, so you don't need to be online "constantly." At most you need to check in about once a day.

* As the white paper says, you can delegate this function to a third party, without giving the third party the ability to steal your funds.

* If the other party tries to steal your funds and you catch him, you get to steal all of his funds. So in practice I don't expect this to be a common situation. If the other guy believes there's at least a 90 percent chance that you'll check the blockchain on any given day, then the expected value of broadcasting a revoked transaction is going to be heavily negative.

[lalaland1125]

One interesting comment about the third point is that once a channel gets sufficiently depleted (say down to 10% of the balance on one side), then there is an increased incentive to cheat (because the potential losses are lower). So you will usually have to keep channels at above a certain balance for security reasons.