Tesla is paying for the data so I doubt you will ever see hotspot capability until that changes. Saying that other cars have it is not a fair comparison because no other car maker pays for data for a web browser, etc. and a hotspot (or at least that I am aware of, perhaps someone will correct me but I doubt it). I'll take the free data and no hotspot capability. If I need a hotspot, I use my phone.
On ATT, hot spot is not part of 4LTE, it is an option on their network. When one turns on Hotspot on the Phone, it say validating that the SIM has the authority. I would doubt that Tesla would have open-ending cost on having a hot spot capacity on each vehicle.
If I understand correctly, the UI doesn't permit video streaming in the Model S. If that is the case, then the data is somewhat limited to Browser pages and OTA software updates, etc. I yield to those with more knowledge on the UI...
Not sure about video streaming, but audio streaming is definitely supported (e.g., TuneIn Internet radio, Slacker). With Radio Paradise on TuneIn, I'm not sure I'm going to need anything else.
BTW, the FCC ruled that a wireless service provider cannot charge extra to enable the wireless hotspot feature for consumers. This directly affected Verizon customers who previously had to pay a separate fee for the wireless hotspot feature. Now anyone on Verizon with a phone that supports Wi-Fi hotspot generation can do that for free (though the data charges still apply):
Verizon worked around the issue by clamping down on unlimited data plans (and eliminating those from corporate accounts, even if you were "grandfathered" in). Not sure how AT&T handled it. Also not sure whether this ruling would apply to the specific plan that Tesla has with AT&T for in-car 3G and LTE. It's likely that it does not apply - they probably made the car's data receiver incapable of creating its own WiFi hotspot. So it would be more of a device/hardware limitation than a "restricted feature."
ATT has and continues to charge $20/month on the data plan (may be used on multiple phones/devices) for tethering or hot spot service. So there is no limits on Apps that use the data as was the case with Verizon. Not sure of the Verizon ruling or difference within the very technical rules. At any rate, it is the use of the data that seems important. With hot spot, there is no limiting factor under Tesla's control on what the hot spot is used for. On my plan (for example of my point), ATT alerts me when approaching the upper limit of my data plan... so if my son is watching NETFLIX, I can turn his data off until the end of the billing period. It is under my control to manage. Tesla could have the same, but I don't know why they would want to manage 200,000+ devices every month.