Pop Songs Ripping Off Classical Tunes

Song writing should be easy. I dislike poetry intensely but a song is pretty much half a poem with a few lines repeated again and again between a couple of four or five line verses.
The problem i have is i sing like a donkey with its head in a bucket and any original tune i get in my head quickly morphs into something well known so writing a song i have never really given any serious thought to, other peoples are much better. 
That is exactly the conversation i was having today with a music teacher when i mentioned the bit about any original tune rapidly degenerating into something else and she casually beckoned me to follow her to a conveniently placed piano and told me to name the song.
She began playing the Elvis tune ' Can't help falling in love with you' and then the classic 70's love ballad 'All By Myself' by Eric Carmen.   
I guessed correctly and she nodded and said what about these and then played exactly the same tunes again, this time they were not a classic 70s ballad and a heart tugging ditty from the shaky hipped one but a turn of the last century concerto by Rachmaninoff and an 18th Century Orchestral arrangement.
The knockout blow was 'Go West' but not by the Village People or Pet Shop Boys but by Johann Pachelbel's and called Canon in D Major and played slighly faster.
Apparently, pop stars have been ripping off classic tunes for decades, either speeding them up, slowing them down or just crossing their fingers that nobody notices that the music is lifted directly from the middle of some symphony or other.
Barry Manilow and even Billy Joel have used half known classical tunes in their songs but it was Green Day's Basket Case which done it for me, they just sped up Johann Pachelbel's Canon in D Major, the same song Go West is, replaced the violins with guitars and drums and sang a song about cracking up and being paranoid.
Of course it doesn't solve my problem of sounding like a frog in an upturned bath tub but i'm sure i could download some free software and add a few guitars and drums to a bastardised version of Finnicule Finicula (one of the best tunes ever created) and write a classic Christmas song.
I probably couldn't actually but someone could and arguably the hardest bit of the song, the tune, is already done for them. 
Gutted about that Eric Carmen song as well, completely ruined it for me. Shame on you Eric.