For bottom-fermented beers the conditioning/storage temperature is crucial and supposed to be really low (32F / 0C). Is this the same for top-fermented beers or is conditioning / storage at higher temperatures acceptable or even called for?
The question is a little ambiguous because the term conditioning is used to mean two different things. Conditioning in the bottle is sometimes refered to as the process of naturally carbonating the beer. (adding a little sugar back to the finished beer prior to packaging for the yeast to use in the generation of carbonation), trapped in the sealed package).
Here however I believe the original author is meaning conditioning from a maturation standpoint. The usage of 'condition/storage' suggests this to me.
For lagers (bottom fermenting) the beer is usually only stored at the 32C range while still in the bulk format. Usually done in a secondary fermentor. For both ales and lagers, the temperature of storage is usually kept below 55F or cellar temp (as mentioned by markskar).
However, the longer you want to store any style of beer, the cooler you should keep it. So standard fridge temps at 45F or less is a good idea.
The mid-50's to low 60's is about what you'd want to bottle condition an ale. Lower temps could cause the remaining yeast to go dormant and not carbonate the beer adequately.
As far as storage goes, it depends on the style in most cases. IPA's need to be treated like deli meat--you want to drink it fresh or the hop character will start to fade. Higher ABV brews can be stored for much longer if kept at cellar temps, and can develop more complex flavors over months or even years.
Generally speaking, for long term storage (greater than 6 months) you'd want to cellar below 55 degrees, but not too cold or the beer may not mature very much.
For short-term storage after bottle conditioning, any reasonably cool (low- to mid-60's), dark place is good, and colder is fine too.