He's connected to a program that allows him to see through his securitrons and send out packets of data that I assumed were pre-set. What I meant is he would need a physical computer to actually create the code, and the factory to put the code onto a device readable by his primary computer in the Lucky 38. If we assume he can create code himself and transfer it to his computer for relay, it does create a problem to the story. Though I don't think the evidence supports that he can do that.
The impression I got (and this is up for debate) was that his control was limited to an interface he had already set up, so all he could do were things that he had pre-programmed in. For example, "Shut off securitron 105", or "Take direct control of securitron 83". If we take it for granted he has semi-normal access to a supercomputer, it does start to pose problems. Though considering how special the platinum chip was, even before the war, one can assume that programming something as sophisticated as a combat system AI in this universe would require a skilled team, not one brilliant man.
He's plugged into a physical computer. We know he can write documents - he wrote the NCR's surrender terms in the House Wins track. Since we know he can create text documents, all he needs to be able to do is run a compiler program and have it read the code in the text document.
We're also not talking about creating an AI - the AI is created, it just needs to be told how to fire the weapons. We're talking about just creating the driver to access it. New OS isn't always required for new Hardware. I'm not saying the new OS isnt better, and is probably designed to handle those weapons better, but I'm surprised he didn't create a work around given the amount of time he had, and the likely possibility that the chip would be irrecoverable (this is a guy that knows the odds after all).
House's goal isnt just to sit where he is, he's looking to start a space program and start space colonisation which he thinks he can establish in a century. If he cant create new programs to handle new functions and situations, he's going to be limited to just sitting tight where he is, he wont be able to directly control any of his future creations (and he's not going to like that - the guys very much into control);
Edit: Further, if he can write out code that sophisticated and relay it, why not write out code to lock access to Hoover Dam to anyone but him? Why not access a few of his Robco factories that are still intact and see if he could get some sentry bots under his control, or get the factories churning out more robots with the remaining materials they have?
House did write some lock out code. You need to install it in the Dam in the House Wins track, and I think its an option in the Wild Card track. Once its installed, House is able to establish control. Given that Hoover Dam is considered an essential piece of infrastructure its going to be locked up very tight from external access thus preventing him from just doing it remotely. Sounds like House has created (or procured from somewhere) a Trojan Horse program to allow him full access through firewalls (or the Fallout world equivalent).
As for the RobCo facilities, they're not in great shape. Even if they are useful, House's current broadcasting range at the start of new vegas isnt enough to establish control - he couldn't even get a strong enough connection to control Victor enough to attack Benny when he shot the courier. This is due to the Lucky 38 reactor being offline (a problem resolved with the installation of the override chip in the El Dorado Substation).
Oh, and he does mention that he has to revert to a dated version of his operating software due to the system crashes caused by the great war.
Which he's had time to look at and fix. Regained conciousness 2168, made his presence known in 2274,