If a user selects Java in Tools/Options/Advanced it should be used also by newer LO versions when it is still supported.
LibreOffice 4.0.0 uses the default java because it updates the list of supported JREs in ure/share/misc/javavendors.xml. It does not check if the old JRE is still supported.
The current behavior causes bug reports about broken configuration migration, for example see https://bugs.freedesktop.org/show_bug.cgi?id=57061#c78 . I think that we could do better job here.
In addition to Petr's comments, this means that if a user has both Java 6 and 7 installed, the setting to remember the selected Java is not imported.
Obviously this will no longer be needed when all scripts are ported to Python :)
Is this still an open request?