I agree with you about time, and would add that it's too precious to spend much of it on Facebook. However, it's nice to at least be aware of the events that are taking place and have the ability to make the choice to go or not.
I also agree with most of what you say - I'm even of the same generation of letters being cheaper than calls, no email, etc. I was just presenting the facts as I perceive them currently. I'm sure that each person will react and respond to those facts differently. Some people may not want to miss out on anything, while others may actively want to miss out on most things.
Regarding email, perhaps I didn't express my idea very clearly. The root of what I was trying to express is that, like it or not, email and the various types of facebook communication all have a different perceived value and importance to recipients. I would think that most people feel that an email is more deserving or demanding for a reply than a mass facebook invitation or post (I could be way off on this, though). And if one sends out a mass facebook message, but only sends an email to a couple of friends that are not on facebook, that puts even more pressure on the email recipients to reply than the facebook friends, just because of the difference in numbers making the email friends not be able to hide among the crowd. Because of this, a facebook user may choose not to contact the email only friends, to not place pressure on them to respond. I hope this makes my perspective a bit more clear.