Why do motorcycle batteries have such short warranty periods?

Looks like I'll be buying a battery for my KTM. I've replaced motorcycle batteries before but never took any specs into consideration I just went with a stock OE replacement. This time around I'm looking at options for dropping weight, increasing amperage, and not having to do this again in a year.
Buying -
Am I right to understand that if my bike requires an 8AH battery, that most likely a 10AH won't fit? The 8AH is already SNUG in there, but who wouldn't want more amperage/longer life? Reading battery specs it looks like any time you increase in capacity, the size goes up as well.
Why do motorcycle batteries have such short warranty periods? Do certain brands offer a year or better?
What's up with lithium units? Who makes good stuff? Worth it to save 5lb?
Troubleshooting -
When testing a motorcycle battery, will a standard 12v battery load checker operate as normal on one, or not since the amerpage is so low on them?
I know squat about motorcycle electronics - when idling, does the stator charge the battery to 14+VDC just like an alternator does a car battery?
My supermoto has a kickstarter on it and when the bike died last night, it wouldn't bump start or kick start. WTF?! I thought the purpose of a kickstarter was to get the bike running in the case that the battery was dead. Upon that, does it sound more like my stator is shot, and wasn't charging the battery?
If it calls for an 8AH, put that in there in. A larger AH battery isn't going to increase the life. It'll just last longer with the headlights on and the key off. 8AH, in short, means that the battery will discharge in an hour with a constant and continuous 8amp load. Paying attention to AH specs is more important when dealing with deep cycle apps. Automotive batteries aren't mean to be discharged in that manner.
Loadtesting. Your load tester will have an amperage rating, mine is 130a, excessive for a lil bike battery. So an alternative is to pull your ecm fuse, crank the engine and monitor battery voltage while cranking. Cranking the engine is used for load testing because the starter motor is the highest strain on the flooded motorcycle battery. If you have a fully charged battery, approx 12.6, it shouldn't drop much below 10v under load. Or just take your static voltage and divide by 1.25. Example. 12/1.25=9.6v