The ADA Amendments Act of 2008 responded to a series of Supreme Court decisions that had interpreted disability under the original ADA more narrowly than Congress intended, excluding some people whose conditions were mitigated by medication or assistive devices. The Amendments Act directed courts to interpret disability broadly and in favor of coverage.
While it does not add new digital accessibility requirements on its own, it matters to web accessibility practice because it widens who qualifies for ADA protection, and by extension, who has legal standing to raise a claim about an inaccessible website or app.