Posts like these that claim there is no difference in portability between various Mac and non-Mac laptops are missing the point.
The size and weight of a laptop is big deal to a lot of people, and depends entirely on individual circumstances, usage and preferences.
For example:
How much do you carry your laptop? From your bedroom to your lounge? From your car to the elevator? For a 15 minute walk from the train? All day between meetings? For days on end on a location shoot in the mountains?
All of this matters!
I have a rMBP 15 which I upgraded to from an MBA 13. In a laptop or shoulder bag, the weight difference is noticeable. After a day of carrying, my shoulder is sore. In a backpack with my lunch, a drink, a jacket, some books & papers, disk drives, power supply etc., the weight difference between rMBP 15 and MBA 13 is less noticeable - because I'm already carrying 3 times the weight of the computer, so the percentage difference is hardly noticeable.
If I am carrying the laptop by itself between meetings in my office building, or to the coffee shop, they the difference in weight is significant. I can't easily hold the rMBP 15 open in one hand to show something to someone when standing up; I need a table or to sit down and use it on my lap. The rMB can be held up without effort with two fingers.
I have colleagues who have "workstation laptops" - quad-core i7's with 32GB RAM, 2 SSDs, and 17" screens. These machines weigh 7-8 pounds, have a power supply the size of a brick, and they often have a wheelie-bag to take to move them around to avoid back strain
It's horses for courses.
So to clarify, the rMBP 13 or Asus ultrabook is not "just as portable" as the rMB, in either absolute or subjective terms. They are less portable. Maybe not *much* less portable for you, but that is subjective.
You may not think the compromise between weight and power / ports is worth it to you. And this is absolutely OK! But please bear in mind that other people have different priorities and values, and it is their right to have these without criticism.
Apple have done a good job designing an extremely lightweight computer, and will almost certainly sell a lot of them. The design lessons will benefit other product lines in due course. I would personally love my rMBP to have the same features but weigh a lot less!