Recently, I responded to Ranger's post re: PC reliability. To summarize, it's up to the person designing and administering the overall system on whether a PC based system is not as, same as or more so reliable than an embedded controller. If you treat the PC as a controller and source your hardware, software, update process, hardware maintenance as such, then it IS an embedded controller that is reliable enough to accomplish enterprise level security and reliability. If you treat a PC as a desktop PC, then you will have the experience that may have drove your question. In general when you buy a proprietary embedded controller system, someone else has done that homework for you so it "appears" to be "more reliable". The other tidbit was once the system is doing what you want it to do, leave it alone and allow it to do that job. Don't dink with it, or you may open a door for unplanned issues.
Sorry I know this discussion has happened before, but it's hard to not respond.
By shear MTBF statistics alone you could argue an embedded system like an Omni is much more reliable than a PC, some of these have been running untouched in people's homes for nearly 20 years. This has somewhat to do with lack of moving parts. A PC with a fan and hard disk will fail simply because one of those moving parts will fail. You can eliminate these things now with fan less power supplies and SSD's, but you are quickly getting into pre-built embedded design "PC's" in order to get power envelopes and passive cooling designed properly for adequate reliability.
Second is complexity, an Omni board is a computer, having all the same components of a PC(CPU,memory,non volatile storage, an OS, user defined programs) but the hardware is much lower power and simply has less components to fail total with a hardwired power supply. The software is also much much simpler, which mean less lines of code to debug less "moving parts" in the software to go wrong, versus a PC running windows which in shear lines of code is many orders of magnitude larger with a track record in bug fixes/updates to prove it.
Third is slower progress, a embedded controller like an Omni is updated (both hardware and software) much more slowly, this can be frustrating waiting for new features, but new features introduce bugs, and these panels are UL listed fire/burglary systems, a bug could mean a smoke detector won't sound the alarm, sorry you will not find a UL listed PC based fire/burg system that doesn't have a embedded "panel" that does the heavy lifting there is one reason for this RELABILITY.
I look at it this way, my Omni panel is like the lower brain stem, it's the autonomous nervous system, handling the critical functions of my home(security, fire, lighting, HVAC, dial out alerting, irrigation). My home server on the other hand is the higher brain functions(Web access, media storage, pc backup, email notifications, complex higher order automation rules). My home server can go down and the basics/safety systems still function. This setup has worked by far the best of anything I have tried and with the cost of these panels now days, it simply not worth it to try and get by with a PC only system.
I hope the day comes when a PC can be a reliable as my Omni, In my opinion that day is not here.
BTW I use Google Sketch-Up, free and powerful, but not as easy to get a floorplan as program designed just to do floorplans like say Punch.