With the relatively small cavity in a microwave you could put less items in, but definitely heat them for a much shorter period of time if there is some reason that a faster kill is needed. A dryer could hold a lot more articles of clothing, several pairs of shoes, a backpack or computer bag, and anything else that could be tumbled and subjected to heat for a half hour. And, I'm just not certain what off-taste that pair of gym shoes might impart to the next bowl of soup you heat in the microwave. 

In the past the recommendation for clothing, shoes, drapes, bedding, etc., was hot WASH followed by hot dryer cycle, but it has since been recognized that the hot wash is not needed, unless of course things need washing anyhow due to filth left on them by the bugs. Bed bugs are extremely susceptible to high temperatures and some numbers provided years ago showed that you could kill all bugs and their eggs within 24 hours at 108 degrees Fahrenheit, in just 60 minutes at 113 degrees, and in just 5 minutes in a dryer at 175 degrees, although leaving it for 30 minutes was better insurance. The suggestion that we could put everything into black plastic bags and leave them in the hot sun has a problem. The bugs move rapidly and may be able to tuck under things at the bottom where the temperature does not get high enough to kill them. The same goes for storing everything in a close truck or storage container in the hot summer sun. 

It also has been found that the use of the dichlorvos (vapona) strips called Nuvan ProStrips is enhanced if the sealed chamber can be heated. The higher temperature may help to volatilize the vapona more rapidly or it may make the bugs take it into their system more rapidly. But, while the Nuvan label calls for treating items like electronic equipment for 1 week, some experts suggest that 2 weeks is more certain, but raising the temperature to over 80 degrees can shorten it more to that 7 days of exposure.