We have kept our house at 67 all winter, down to 66 when my wife felt the need to cool off a bit.
Temp differences won't be detected by electronic devices but operating temperatures will be.
The only time "differences" come into play is when devices cool down, heat up, cool down, heat up, etc. Heating and cooling cycles. This can cause component stress and in some cases where sockets are used, component "walk" where a part will literally rise up out of the socket in rare cases (very rare these days with so much surface mount stuff)
I used to work at an electronic engineering and manufacturing company, Compressor Controls Corp, I designed the control interface computers and set up the environmental tests - the devices would be heated up, then cooled down (we had a large nitrogen tank sitting outside of the manufacturing department test area). There was a chamber where the electronic control systems were placed and subjected to temperature extremes while running a battery of software tests I devised - intending to stress the hardware as much as possible while it also underwent the extreme temperature changes. (thrash a hard drive hard while heating and cooling it for example)
The devices won't care what the ambient temperature is unless it's so high that the device can't cool off. There must be a temperature difference in order for cooling of the hot components to take place. The less difference there is, the less cooling that can take place. It's sort of like the radiator in your car. If it's super hot outside then the cooling system can't remove enough heat and the engine runs hot. Same for electronics - I used to have an office with no AC and in the summer the room could reach 100 degrees - the computers would periodically lock up, but cool the room down a bit and the computers could release heat more efficiently and they didn't lock up.
With passive cooling of electronic devices you WANT a temperature difference, the more the better to some extent. If the temperatures and humidities change a lot, wild swings, you can get things wet with condensation and cause major issues that way, like taking your digital camera outside on a hot humid day after it's been sitting in a cool air conditioned house - it will get wet inside! But that should not be an issue with Tablo unless it is in your basement or in your attic in a climate like Iowa or MN would have.
Seriously, it's the lack of ability of Tablo to rid itself of heat with the the totally passive cooling it has that is or COULD be a problem, not how much difference there is between Tablo and the ambient or room temp. Within reason, the more difference the better, and I mean the room being several degrees cooler.
With our house at 66 to 67 degrees I've had no Tablo heat-related issues. It might have helped that I also sat my Tablo quad up on an aluminum heat sink I salvaged from an old computer so it's off the table, it's got almost 2" of air circulation under it, and the fins of the heat sink help dissipate heat from the bottom of the Tablo since the air vents on Tablo are both low - that in itself is a cooling issue since heat RISES and as the air inside Tablo heats it's trapped, can't get out the top.
I spent 7 years studying environmental considerations of electronics as well as packaging and shipping since our controllers were shipped from Central Iowa to all over the globe including Eastern Europe, South America, Canada, Alaska, etc.