I feel exactly the opposite! As thenewwguy was saying, this is a complicated question. The word "khmer" means "Cambodian." They're synonyms. "Cambodia" itself is a Frenchified version of "Kambuja" or "Kambuja-desa", for the region. Thai nationalists and irredentists sometimes use the word "khom" to refer to the ancient Khmer, but this is in many texts a way to separate the present-day Cambodians from the builders of Angkor (when they are clearly one and the same). One can't say the same for "Indonesia" and "Majapahit."
To jump to Indonesia, Indonesia was used to refer to island Southeast Asians for a long time, and eventually came to refer to the Dutch possessions (as opposed to the French Indochina). The Indonesians, being an extremely diverse group, chose to adopt the neologism "Indonesia" instead of any of the ancient names for the region - those ancient names would imply Javanese power, and a name like Majapahit would, further, point to a pre-Muslim past (not a popular move for now-Muslim Indonesia). There were no, until independence, "Indonesian people" - there were Javanese, Bugis, Dayak, Balinese, etc., etc.