According to the OpenGL 4 documentation, GL_RGBA2 and GL_RGBA4 have a base format of GL_RGB even though they have alpha bits.
This is inconsistent with the OpenGL 3 ES documentation. Is this due to some sort of legacy issue?
Since this question has no official answer after a week, I'll post on Yakov Galka's behalf.
"They don't; That documentation has a typo. The authoritative source is the OpenGL spec, where in table 8.12 RGBA2 and RGBA4 clearly listed as having RGBA base internal format."