Can't find any decent stats on the matter and while I'm pretty sure a 'professional' burglar wouldn't bring anything much more dangerous than a crowbar or pocket knife, I'm not sure how many pros there are compared to drugged up junkies or gangers who carry guns regularly and just happen to be committing burglary. It would seem really stupid considering the increased penalty but even non-junkie criminals tend to include a lot of dumb people.

There is a reason why one of the standard questions asked during phoned in bomb threats is 'Name and address?'

Still I would bet armed burglars are the minority, I can't recall ever seeing aggravated burglary on the bi-monthly grand jury indictments list locally but burglary certainly isn't uncommon or aggravated assault so I doubt our reporter is too lazy to add on the 'aggravated'. I wouldn't think it too wise to give them the benefit of the doubt though, I'd tend to assume any burglar professional enough to have given thought to the matter is also probably smart enough not to rob a house they have any reason to think actually has someone inside it at the time.

Edit: Kind of an afterthought but it does also occur to me that a lot of burglary arrests probably take place after the event and without camera recording or eyewitnesses, so many could be packing and just not dumb enough to confess it when the detectives show up.