what is oracle universal installer in oracle database products
Oracle's installers are mostly Java based - see here. Oracle apparently wants to "universalize" (yuck, what a word) the procedure. Apparently, however, for XE on Windows, they decided that it would be best just to have a plain old .exe. 

Maybe they figured that Windows users who chose the XE option weren't up to installing a JVM? :-). Maybe they used some sort of Byte code-to-exe tool to convert their Java based installer to a simpler Windows exe?

Apart from the CPU, RAM and data limitations in XE, Java isn't included in the database. If I recall correctly (haven't done it in a while), the Linux installer is a Java based one - even though Java isn't in the db. I'm not sure if the installer has it's own JRE or whatnot. 

Basically, Oracle is trying to make installs as generic (univeralize - what was wrong with the word "generic"?) as possible but has decided to keep the .exe paradigm for Windows.