I make an issue of this as I used to model in a similar fashion to Vardar. After working with and learning from people like Quanto who are professionally trained in modeling, I can tell you why it's important to model in quads. I will also understand why you might opt for triangles in certain instances as well, though.
First, as mentioned, lighting issues. If I was fluent with a full-function modeling program like Blender, putting a fix on the "triangle mess" which is clearly visible in those renders might be less of an issue, but it would still be one more thing I'd need to do. A modeling program automatically triangulates any surface created, and thus automatically adjusts the lighting applied to that surface. Hand-triangulating, which I used to do a lot of, might correct some shape issues (like "dented-in" surfaces which shouldn't be dented in). If you're on a polygon budget, or need to ensure a particular part of the model is not left to chance when it comes to a program's automatic triangulation, that might be something to consider. However, that is probably NOT the case with regards to this model. That said, let me prove my point: anywhere a section has been triangulated, you see a triangle, not a smooth surface. Modeling in quads would most likely clear up this lighting problem.
Next, there's modeling in general. It's a heck of a lot easier to split a square than a triangle. Given that it's not 1996 anymore, polycount isn't too much of an issue, though that doesn't mean you need to be irresponsible with it, either. If there's an area where more curvature is needed, it probably means you need to insert another edge loop. Furthermore, using proper edge loops will allow you to get those nice, flowing shapes which are essential to aerodynamic or hydrodynamic vessels. If you don't know what I'm talking about, here's a wireframe and filled view of a turret modeled in quads - it will be pretty hard to find any triangles in this model.
Just to clarify terminology, an "edge loop" is a linked string of quads which runs over the expanse of a given model. In some parts of a model, it might indeed be hard to pull that off - making sure it can be pulled it off also should encourage a modeler to tactfully place and position every quad and vertex. Doing that in turn should help to ensure a properly and efficiently made model. Vardar, if I was to go back and fix a ship model I was working on for the longest time, the UXV, with a hull modeled in quads and proper edge loops, I can guarantee you that it would look much cleaner and much more realistic. If at all possible, leave triangulation as an automatic issue for PCS2 to fix.
Next, there's UV mapping. If you model in triangles, those edges are a new evil to deal with. That split edge will quite likely cause distortion and unnecessary hair pulling on your end getting that UV into shape. Modeling in quads, you're far less likely to suffer that fate.
Lastly, and this is outside the scope of FS2, modeling in quads is necessary for proper subdivision modeling. Triangles don't split all that easily, but quads do. Thus, when sbdividing a model, you want the outcome to be smooth and fluid. The best way to ensure that is to model in quads.
I hope this helps.