[hider=Something I'd also like to nip in the bud before I start.]
I find people who are against online relationships tend to look at them and go one of two ways:

1) They personally couldn't handle it, so they rule that it's fake or not possible
2) They see the massive amount of those that fail, and as a result call them unstable and think they won't work.

My response to each of the following is:

1) Everyone is different, just because you yourself can't handle one, doesn't mean the rule applies to everyone.
2) Most RL relationships also fail miserably, but we don't go around saying face to face relationships don't work as a result.

Now that's out of the way... I'll get started in responding to your points.[/hider]

First off, I'd have to disagree with the Introverted VS Extroverted bit.

They can be extroverted in that they love talking and interacting.
Like maybe that one friend whose always calling people on Skype, inviting you to online games etc.
Something like that can actually help in an online relationship if for nothing more than to give the couple more things to be doing.

I do agree that not everyone can handle it.
I know when I was in one, the fact I wasn't ever able to see her in person, hold her or kiss her would tear at me beyond belief.
I stayed though because I got more enjoyment and fulfillment out of the emotional bond than the pain I got from lacking the physical contact (and as I learned a year ago, I'm a very physical/close person when it comes to relationships).

Higher expectation of communication?
Generally true, but it would depend on the couple.
There will be exceptions where an online couple could get by with semi-daily interaction.
But I'd say the vast majority need more constant communication in order to keep it going.
This can also lead to the couple being much more emotionally close and connected than they could of been if it was in person.

Also people in online relationships can lie... Many times they do.
When I was in one I was lied too, a lot.
Granted she normally was later on honest, but there was a lot of dishonesty going on before she later of decided to be honest about it.

It's much more difficult to uncover a lie online than it is in person. So there's little to no fear about the results of lying.
Also if they struggle a lot with the online part, they may be already pursuing another way to fulfill the physical aspect that they're lying about.

This can be extremely painful for the other person to go through, and all warning signs say get out of there.
But you're too close to the person to consider it as an option, you trick yourself into believing things are fine or that they will work out.
(Personal experience detailed at the bottom of the post, storing down there in case you don't care to hear of personal accounts).

Online relationships I believe also need the goal of being together in person eventually though.
It could take weeks, months or years. But you should be working towards it.
There isn't too much point if you never actually plan to see the other person and be with them.

[hider=Personal Experience (Why you need to use your head)]

I know after about 2 years of being lied to, made to feel guilty or treated as second option it hurt like hell to leave for good.
It had ended with her basically going "I can't do this now, but maybe later we'll get back together" (This happened a lot, it was on and off), that my heart just shattered and by head leaped into action.

This was someone who was the absolute world to me, they were the thing that made me most happy (and hurt), the one I always thought of, cared for, made priority over all else (Seriously, I had completely prioritized her over my 3 extremely close friends, who astonishingly stuck around till the end. Since we're still friends today even) etc.

But it hit a point where I knew if this didn't end, I was going to keep feeling miserable and dependent. So I got out and completely cut off contact (Until 9 months later, when a grandparent died and I was told at the funeral "Don't let the last experience with those you care for be a negative/hurtful one" so I checked up quickly just to try to make sure there weren't overly bad feelings on either side. But still kept distance and didn't make any efforts to get close again).

I had waited too long to use my head and get out of there, where about 2 years later I still find myself lying in bed most nights, hurting about as much as I did the day it had ended for good. I wasn't able to get out and let my heart be able to recover and heal. I simply had to sever it off from the relationship to prevent any worse damage from developing. Completely removing my feelings from the equation and acting on logic alone.

Granted, this kind of thing could also have happened in real life, but I still say this to stress the point use your head from the start. 
Before you get to the point where you need to rely solely on it to you get out of a bad and painful situation.[/hider]