I've seen many circuits that drive traces directly. With the 8052 the problem is the port pins cannot source enough current and the triac needs to be fed current in order to turn it on. I can only assume the lpc900 series have different port hardware that will source sufficient current as does most other micro controllers these days. A read of the relevant data sheets would've told you this. As previously mentioned, driving a triac in this manner means the micro will be sitting at mains voltage thus making it rather dangerous to work on. The other downside is you need to protect the micro from the mains transients which will kill your micro quite easily. Upside is you get away from using those unreliable optos.

Basically, if you REALLY want to drive the triac from your 8052, then use a pnp transistor and a couple of resistors.