It's no accident that Ali Arikan opens his 30th anniversary celebration of This Is Spinal Tap with a Shakespeare quote (Henry V, Part II's "How ill white hairs become a fool and jester!"). Like many great comedies, Arikan argues, Tap has roots in the not-so-funny, specifically the band's delusions of grandeur, which are cruelly punctured, trampled, and then set on fire.
The band is constantly confronted with evidence of their mediocrity, yet they choose to ignore it. They mistake an approaching gang of groupies for their own, when it turns out their interest is directed towards an Eddie Van Halen-type '80s rock star. They get second billing to a puppet show. The radio plays a song from their early years, but the DJ bookends it by deeming them a second-rate band that enjoyed only middling success. They're sorted summarily into the "'Where Are They Now' File." Life picks them up for a moment, lifts them, but quickly drops them down on the ground. Their fantasies of who they are get crushed by the palpable enormity of reality. Even in the film's most famous moment, when Nigel tells Di Bergi that the band's amps go to 11, the facile stupidity is emblematic of the band's own, almost-solipsistic self-image.
But the paradox of Spinal Tap -- and the key to its enduring longevity -- is that there's a different kind of nobility in the Tap's refusal to come to grips with reality, or rather their ability to push through the ugly truth of their waning popularity and rock on anyway. It's what made the movie a tour-bus favorite in the 1980s, before a more widespread audience caught onto its greatness, and why it still strikes home today, long after its reference points have faded into oblivion. (Having grown up in the era of Poison and Motley Crue, I loved Tap for years before I realized there was an era when the most popular heavy metal bands in the world were British.)
Sadly, it doesn't seem like the commentary to the original Criterion Collection DVD, where Harry Shearer, Christopher Guest and Michael McKean discuss the movie out of character, is available online (although $30 for an out-of-print Criterion is practically a steal) but this fansite has plenty for scholars to pore over.