Tail Skids on 146 & 737's

[HZ123]

I find this one of the most interesting forums on pprune. Why also do some a/c 146 / 737 that I have noticed have tail skids (or what certainly appears to be TS's) yet the same mark of a/c don't. Is it a spec of the first customer to purchase the a/cs? If the skid is effective then why is not a standard fit irrespective.

[Rigga]

Same Reason for 146-200/300's. 146-100 does not need a Tailskid.
Longer aft fuselages give greater risk of Tail Scrapes.