一直这么理解，今天才看到官方的解释，真是有点汗颜。
核心就是 6.0用于平台和产品的名字，而1.6.0用于开发者。 他们指的是同一个东西。
原文地址：http://java.sun.com/javase/6/webnotes/version-6.html
JavaTM SE 6, Platform Name and Version Numbers
At this release, the platform name has changed from J2SETM to JavaTM SE. The official name is JavaTM Platform, Standard Edition 6.
在这个版本里，平台的名字从J2SETM 改变为 JavaTM SE. 官方的名字是 JavaTM 平台，标准版 6.
Both version numbers (1.6.0 and 6) are used to identify this release of the Java Platform. Version 6 is the product version, while 1.6.0 is the developer version. The number 6 is used to reflect the evolving level of maturity, stability, scalability and security of Java SE.
2个版本号(1.6.和 6)都用来标识这个版本的Java平台。 版本6 是产品号， 1.6.0是开发的版本号。 6这个数字用来反映Java 便准版的成熟、稳定、可测量和安全的的程度，
Version 6 Used in Platform and Product Names
版本6 用于平台和产品的名字。
Version 6 is used in the platform and product names as given in this table:
版本6 用于下面这张表给出的平台和产品名字。
Full Name Abbreviation
Platform name JavaTM Platform, Standard Edition 6 JavaTM SE 6
Products delivered
under the platform JavaTM SE Development Kit 6 JDKTM 6
JavaTM SE Runtime Environment 6 JRETM 6
Due to significant popularity within the Java developer community, "JDK" continues to be the acronym for the development kit, as does "JRE" for the runtime environment. Notice that "JDK" stands for "Java SE Development Kit" (to distinguish it from the Java EE Development Kit known as SDK). The name "Java Development Kit" is no longer used, and has not been offically used since 1.1, prior to the advent of Java EE and Java ME.
由于在Java开发者团体里声望太高，JDK继续成为开发工具的缩写，JRE则是运行环境的缩写。 注意，JDK 的标准解释是“Java SE Development Kit"(用来区分 Java EE Development Kit 的SDK). "Java Development Kit"这个名字不在使用，而且自1.1版本以来就没有被官方使用，优先于 Java EE和 JavaMe。
Version 1.6.0 Used by Developers
1.6.0版本则用于开发者
Java SE keeps the version number 1.6.0 (or 1.6) in some places that are visible only to developers, or where the version number is parsed by programs. As mentioned, 1.6.0 refers to exactly the same platform and products numbered 6. Version numbers 1.6.0 and 1.6 are used at:
Java SE 在某些只对开发者可见的地方保持了版本号1.6.0(或者1.6)，或者一些被程序解析的版本号的地方。提示：1.6.0 与平台和产品名为6的完全相同。 版本号1.6.0与 1.6 一般用于：
* java -version (among other info, returns java version "1.6.0")
* java -fullversion (returns java full version "1.6.0-bxx")
* javac -source 1.6 (is an alias for javac -source 6)
* java.version system property
* java.vm.version system property
* @since 1.6 tag values
* jdk1.6.0 installation directory
* jre1.6.0 installation directory
* http://java.sun.com/javase/6 website