OK hee's the geeky bit -
Yeah, most people lose the ability to hear high freq as they age - but there is a lot more to it ...
Sorry to say if you can't hear it when the ad plays on TV, but can hear the ringer, then your TV probably has an amp that just doesn't respond to higher freqs, or speakers that can't reproduce them. I work in live sound, and even though we know that most people abosolutely can't tell, you still try to get the 20 Hz to 20 KHz response out of your system, because somehow it just sounds "better"!
There are a lot of moderating factors - as for compressing/converting - it is certainly possible that you can lose high end - tho I have found that MP3s tend to sound a bit "peaky" (too much high end) , something that you either get used to or you EQ out.....
Anyway,had to put in my 2 cents (pennies - I'm English) worth