the cold to warm is something to think about, especially on systems where the solder may already be fragile, but even that is kind of an extreme, is your house really really cold, does a mac instantly heat up? yes over time it can have effect, but unless there is a design flaw in the machine (early apple ///) this should be well within tolerances

bout the only thing your saving IMO by not using a machine is its exposure to the outside world, course we know of the damages that can happen to the case plastics, but also in terms of power spikes or even "dirty" power which of course hammers the capacitors (which can be somewhat restricted by the use of a really good surge suppressor or ups)

the tv's in bars thing does hold some truth keeping in mind any tv made past the 1980's is mostly empty and heat is not a major issue (it defiantly would be in old analog n tube systems), but it also burns out the crt the quickest