The relationship between Marge and Bart has always been an endearing one, with Marge overlooking her son's defects and loving him in spite (and because of) his shortcomings.
Occasionally, Bart does cross the line and do things that deeply disappoint his mom. But for the most part, he knows the line and does his best to stay on the side that makes his mother happiest.
"The Fabulous Faker Boy" was apparently about the complex relationship between the two, but this theme really fails to come into focus. For a Mother's Day episode, there certainly wasn't a lot of attention paid to Marge.
Instead, the focus was on Bart's crush on his piano teacher, a beautiful but harsh young woman. This isn't the first time Bart's been hung up on older woman. Heck, he was just involved with Jimbo's girlfriend last season. Like many times before, Bart's infatuation leads him to do anything to please his crush. But instead of pulling pranks with the Reverend's daughter, this time he pretends to be a great piano player to get his teacher more students.
And of course his trickery doesn't get him any closer to his beloved. But it does disappoint his parent.
Marge may have been a background character in Bart's piano lessons (giving driving instruction to the teacher's father as payment), but she was pushed to the forefront when she arranged another recital for Bart out of pride for his talent. This caused Bart to confess to his lies, letting Marge down yet again. It's not until then that we find out it's Mother's Day.
Not only was the mother-son dynamic shoved into the narrative late in the game, but Marge's disappointment was easily waived away by her Russian driving student saying Bart cheated for love and for his mother. Kind of a simple rationalization, right?
The B-plot involving Homer's loss of his last two hairs did lead to some hilarious The Simpsons quotes and an amazing guest appearance by Patrick Stewart (one of the sexiest and most confident bald men), but it was mostly a distracting vehicle that allowed Homer to try on various hats.