Because with a thunderbolt port you could operate all three of those USB3 ports and at full 5Gbit speeds and the gigabit ethernet port. You can't do 3x USB3 speeds on a USB3 port.
Without a lot of cost, without Thunderbolt you aren't likely going to get that anyway. Even on many computers, not each port gets it's own controller. There are often internal hubs and the like. More than likely, any USB hub with it's own controller (like a thunderbolt dock) is going to have just one controller and thus just one 5gbps connection.
Besides, there really aren't a lot of use cases for that much bandwidth. A FAST spinning hard drive will hit maybe 120MB/s (960mbit). Even an SSD won't saturate 5gbps. The only time you'll saturate even one 5gbps connection, or even come close to thunderbolt, is moving tons and tons of files through a large RAID enclosure. I don't think people realize just how fast USB 3.0 is. I think it's part of why Thunderbolt hasn't taken off yet (though I'm not going to call it 'dead' like everyone else who apparently got their very first computer in 2009. Ever major new standard, even USB, took several years to really take off.) is that there really aren't a lot of uses for it yet. USB 3.0 is fast enough for external storage in far more applications. An array of SSD's or a huge array of fast spinning disks, perhaps. Otherwise, with just about any single disk, USB 3.0 is fast enough.
However, USB has always been notoriously over-represented. USB 2.0, for example, had a 'signaling speed' of 480mbit/s. but could only actually transfer data at 280mbit/s. It's all marketing. That's why FW400 was far faster than USB 2.0 (despite USB 2.0 being '480' vs '400'). So I'm not sure how much ACTUAL bandwidth you'll get. But I know I'm able to get full saturated speeds with my external drives.
EDIT: The ACTUAL speed of USB 3.0 is 3.2gbit/s, and it's maximum payload throughput is 4gbit/s using a certain type of encoding (just looked it up!). Even that's plenty fast enough though for a couple hard drives, given that most use cases aren't pulling down large files from multiple drives at the same time. Though, I still hate that something that can't hit about 3ish gbps and, only with special encoding in a synthetic environment can hit 4gbps, but be marketed as 5gbps. What if cars were marketed as getting 'up to 100mpg' because, in a vacuum tube at 19mph they can get that?
Makes me wonder if Apple would have been more successful with FireWire if THEY lied about the bandwidth (or used the maximum electrical theoretical throughput, which the hardware could never actually achieved). On paper, FireWire always seemed slower. But in the real world it's much faster, as it nearly hits it's advertised speeds.
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So you dont really know what the problem is then
I was talking about using a USB 3.0 hub, with USB 3.0 devices plugged in - none of them work correctly on the rMBP. The second you plug in any additional devices that are USB 2.0 the whole thing falls back to USB 2.0.
Apple's implementation of the USB 3.0 standard is flawed.
That's really really odd, for two reasons.
1, the 'standard' for USB 3.0 includes 2.0 backward compatibility. Though it might make sense if Apple is only using ONE controller that perhaps that's happening.
And 2, I'm 99% positive my non-retina doesn't do that. Just the other day I had one USB 2.0 connection to my cinema display, and another to a USB 3.0 hard drive and was transferring a big batch of files.
Edit: Yep, no issues here on a mid-2012 non retina. USB 2.0 works alongside USB 3.0 with no speed decrease. Although it's worth noting that I'm getting 650mbps to an external 2.5" drive, wheras I can reference my NAS at about 900-950mbps over ethernet. Further reason why I really think USB 3.0 is an over-hyped standard! Maybe I'll take back what I said before, I assumed that it would run about half of it's advertised speed like USB 2.0 did, which puts it as fast as eSATA. But that's not the case, at least from what I'm experiencing and others have reported on the 'internets'.
