If you take a look at MySql Administrator, then you'll notice that it is meant for administering MySql DBs only, while SQLyog is lot more then a simple admin tool. SQLyog offers additional synchronization and import tools, the possibility to issue SQL statements. I must aknowledge, however, that the administrative capabilities of MA exceed those of SQLyog, especially in the field of startup parameters and server logs.
Hopefully the long-awaited SQLyog Max will give a sufficient response to the challenge!