I overwinter mine indoors every years at normal room temperature and they never fail to bloom, usually as soon as I return them outdoors in spring.

Really? But what are your "normal room temperatures?" I keep my thermostat on 70 F all winter long. I was told that if they didn't get exactly what they need, they may not bloom until late summer, and I'm fine with that. My main problem is not having enough shade for them, but I'm going to try to create a sort of lattice house for my shade plants this year.

I have no idea as I don't control or even see the thermostat (rental unit). But it is far above 50F!! I sometimes have to open the door even in winter as my elderly landlady likes it hot!

When I first started growing clivias maybe 35 years ago, I grew them inside year round ad normal room temperatures. And they bloomed annually every year in late spring. These not nearly as tricky or difficult to grow as you may think.

I think maybe the not watering is the most important part, from what I'm reading. Maybe I'll just grow them indoors from now on, and not worry. Only 11 more days until I can water and fertilize! I have two in each pot. I think I'm going to separate the smaller ones and put them into their own pots this year.

I see Barbara Pleasant, Complete Houseplant Survival Manual (2005, Storey) describes them having the same requirement you mentioned here.

A special temperature regimen is needed to make a clivia bloom, but this is easily accomplished by keeping the plant outdoors in fall during the last month before the first frosts arrive, and then moving it to your coolest indoor room and keeping it rather dry until midwinter. After this cool, dry rest, a gradual increase in water, coupled with normal room temperatures, leads to a beautiful show of blossoms in February or March

http://www.bing.com/shop?q=complete+houseplant+survival+manual&FORM=SHOPPA&originIGUID=5E411E2F3E8D4CC284BF641D293300CE

I didn't ever get "a beautiful show" from mine, rather one or two clusters each time. Well below the leaves and off to the side.

The basis for plants and seeds needing seemingly special or peculiar conditions like this in cultivation is how they have come to react to the climate of their native area, with there being times of the year when it is not suitable to be doing something like sprouting or blooming.

Watering may indeed be a factor.......more so than a need to keep cool. I water mine maybe every 6-8 weeks in winter, no more frequently than that. But it is in a pretty good sized container. I don't start watering again with much regularity until the plant gets moved back outside.

@Embothrium(Pugetopolis), @gardengal mine were outdoors in the fall until October, and I tried to leave them longer, but it kept raining on them, so I brought them in for the rest of the winter where I could control the water. They've never been in 50 degree weather, because it doesn't even get down to 50 at night in October. Oh well. I'll give them one more year and if I don't get blooms, I'll sell them to someone who has better conditions.

In addition to a dry (virtually waterless) stretch in winter, cool temps are generally needed to promote flowering. I left plants outdoors this fall until temps were getting close to freezing, brought them indoors, then took them out to the garage for a ten-day stretch in which it was getting down near freezing, then back inside. One clivia is about to bloom for the first time, while I'm waiting to see what happens with the other seed-grown mature plants (a yellow-flowered hybrid flowers faithfully every year even without special cool treatment).