Yes, there is no natural cap or limit that we've been told, and it's linear progression.
But it's very simple to understand, which I think is key. They could implement a log conversion, or simply cap it at 10k or some arbitrary number, but that only makes more special cases.
Since there's a limited number of votes, everyone is policing everything, and there are limits to how many questions you can post (ie, once every two minutes or similar) then the damage a high point hacked account can inflict will be little and can be handled by the community.
Now, if someone hacks the top 50 accounts, they could probably ruin the front page for a day or so until Jeff shuts them out...
But I don't think it's a problem. The DOW just keeps going up, right? Why not stackoverflow reputation?
Besides, if you cap it (aside from eliminating e-size measurements) you also reduce some people's desire to answer questions. There are questions I answer only because I haven't hit my daily cap, where I wouldn't have because it takes some work and time to do right.
There has to be some payment for good work...