Hello Kian,
I think a possible explanation is that PPP multilink includes fragmentation service: the added delay tries to take in account time for PPP reassembly.
Delay is an administrative parameter so they decided to put it to 100000
I can say I see same values on a router of mine
sh int multilink1
Multilink1 is up, line protocol is up
Hardware is multilink group interface
Internet address is x.y.240.150/30
MTU 1500 bytes, BW 4096 Kbit, >> DLY 100000 usec,
reliability 255/255, txload 1/255, rxload 5/255
Encapsulation PPP, LCP Open, multilink Open
with IOS version
sh ver | inc image
System image file is "flash:c2800nm-spservicesk9-mz.124-3i.bin"
this has a clear impact on EIGRP routing and so you need to manually adjust delay for your needs
Hope to help
Giuseppe