1) LG magazine (10 to 15)
2) Med to LG cal.
3) Durability (does it have a reputation for fireing unexpectedly)
4) LITTLE OR NO PLASTIC ( I used to play with toy guns....)
5) Med to light weight
6) Decock
7) Grip safety
First off, I love my XD. It was my first semi that I bought. I have been shooting guns my whole life, and spent about a year prior to purchasing just shooting different pistols (I'd estimate 1,500-2,000 rounds total). I kept a "diary" of all of them, just to ensure I remembered my thoughts on them. For the price, feel, durability, company reputation, ect, you can't go wrong with the XD. As I mentioned, I shot all manner of Glocks, 1911s, Sigs, FNs, CZ, Berettas, ect, and found the XD40 Service to be the best overall.
1) Standard is 12 (unless CA, then 10), so that fits in there perfectly. There are many aftermarket extended base-plates that can add 4 or so more rounds. There's a 20-rounded you can get (Once I added the +4 base-plate to use when bump-firing. Can't get much more higher capacity than that). I have many of them, and they work flawlessly. I don't OC with them tho; just at the range.
2) .40S&W fits that. I would probably consider it a large pistol caliber (medium if you're looking at calibers in general). Packs more of a punch than the 9mm, but can fit more than the .45. Not gonna resurrect the caliber war here, but the way I see it, if it was a bad round, it wouldn't be so popular.
3) That it is. As someone stated, hence the "X-treme Duty." Can't find it right now, but I stumbled across a blog/website, where they did the Glock torture test, but with at least 5 times as many rounds for every stage. This totaling about 20,000 with almost no cleaning.
4&5) If you don't want plastic, then it's gonna be a heavy gun. Conversely, if you don't want a heavy gun, you're gonna have to have plastic. All I can say is, the XD polymer is extremely tough. On the off chance that a factory round blows it up, or a manufacturing defect caused weak plastic, Springfield will be more than happy to make it right.
6) Why? I personally don't see any reason for these. It is possible for these to fail and render your gun nonoperational. Then all you have is a pretty looking rock. I want the fewest things that can go wrong in a life-and-death scenario. If you're uncomfortable carrying a firearm with a round in the pipe and ready to fire, then frankly, you shouldn't be carrying. These guns are made to not go bang unless you have a proper grip and pull the trigger. Learn how to use your firearm, how it works, and the only safety you will need is your brain.
7) Similar to #6. I don't see a reason for these. At least with grip safeties, you don't need to think about disengaging them. Also, they are almost 100% fail-safe, meaning if they fail, only the safety is affected. The firearm will still operate.