I've personally made beds with the following hardware (sorry for posting links to a Canadian store - I'm still working out where to buy stuff now I'm in the UK).
Mortis bedlocks - These were of the same type the original question was asked about. I've not had any troubles with them coming loose on the endgrain, but I did make a point to make the mortis fit the fixture perfectly. Fitting the mortis properly provides quite a lot of support to the fixture, and after a couple of years of use there was no compression of the wood fibers around the fixture (which would indicate some level of movement). I used white oak - I'd feel less confident if I'd used a softwood.
http://www.leevalley.com/US/Hardware/page.aspx?p=67916&cat=3,40842,43730&ap=1
90 degree bed rail fasteners - I've used these for a quickie knockdown bedframe once. They were very easy to install, locked everything up very tightly, and they worked well. It was a bed used in a spare room though, so it didn't get an enormous amount of use. I was always a little worried that everything rested on just a few screws, but I didn't end up having any problems with them. Time in use - 3 years. Pine.
http://www.leevalley.com/US/Hardware/page.aspx?p=67917&cat=3,40842,43730&ap=1
Mortis-free bedlocks - these I've used as well, and again they were fine. The bed in question was for a friends spare bedroom. No real issues with them, they worked just fine. Not my favorite, but they were inexpensive and did the job so I don't have any complaints. I was still worried about how they'd hold up, as like the ones above they rely on the screws to hold everything together. Time in use - 4 years. Ash.
http://www.leevalley.com/US/Hardware/page.aspx?p=65401&cat=3,40842,43730&ap=1
carriage bolt and barrel nuts - my personal favourite, use 'em all the time for beds and workbenches. They do loosen up over time, but it's a 60 second job to tighten them all up again once a year. The downside with regards to OP's question is that they can be seen as the carriage bolt sits in a countersunk hole in the bed leg. That hole can be covered up with a removable plug or a decorative medallion, or whatever strikes your fancy... but it will still be visibly different from the rest of the leg.
I buy mine from fastener supply houses or (most recently) on e-bay. Depending on the size of the stock I'll used anything from M6 to M10 - and buying the barrel nuts (also known as cross dowels) in bulk saves you a boatload of cash. The carriage bolts I just buy anywhere, but I recommend getting a hex-headed bolt you can ratchet instead of a head slotted for a screwdriver.
a link to a set on Lee Valley - but again, I'd recommend just sourcing the parts locally.
http://www.leevalley.com/US/Hardware/page.aspx?p=40445&cat=3,40842,43730&ap=1
There are a few other common bed lock hardware types you can use, but I've not had any experience with them personally so I can't really comment on them. Some look very cool though.
If I'm making something for myself and I have the time, I'll use mortis and tenon joints (preferably tusk tenons). If I don't have time I'll use carriage bolts and barrel nuts.
dak