Nostalrius Begins - Quality wow vanilla realm (1.12)

The 10-19 battleground bracket was not released until nearly a year after launch.

Players of levels 10 - 19 will now be able to participate in the battle for Warsong Gulch.

Source: http://www.wowwiki.com/Patch_1.8

Patch 1.8 is not "shortly before the burning crusade", it was over a year before TBC came out:
1.8.0 Release (US) 10 October 2005
2.0.1 Release (US) 5 December 2006

Nostalrius has 1.12.1 talents, spells and abilities with mostly pre 1.4 itemization. Disabling the 10-19 bracket for WSG for a month or two is not very high on the list of things to do for the small dev team that the server has.