It's definitely not worth buying for a rental.
I will disagree that a motion detector is enough. Nest has a bunch of algorithms for different heat setups, and it learns how fast it can heat/cool your house using different controls. It knows the weather, so it can predict ambient temperatures. It knows how cold or warm you can go without complaining based on your usage - you might program a cheap model for 73, but nest realizes you don't mind 74, and eventually 75. It knows how much it costs to heat quickly vs slowly.
And it knows the difference between people at work, and people sleeping, and people off on vacation, and so on. Went out to the park and forgot to turn the AC down? Just pull out your phone and tell it you'll be back at 6PM, so it can decide when to set what temperature and how fast to do it. And so on.
Oh, and it gets firmware updates over time. Better algorithms. For example, it can now detect that its thermometer is being hit by a sunbeam and doesn't think the temperature spiked. For example, it will interface better with utilities in the future.
It's not about being lazy, it's about cost savings you *can't* do by just walking to thermostat and adjusting it, as you put it. It's not about wanting to spend cash on a fancy gadget, it's bought solely because it should have a fairly high ROI - just like an energy-efficient fridge, or LED light bulbs, for example. I got one for my parents, and they already kept the house pretty cold in the winter and so on, but it's managed to save them a pretty penny that they had no idea could be saved. (I got them version 2.)
Most people already have a smartphone and a data plan, but you can also use your work-supplied computer at work, if you so choose.