[XeTeX] ICU 3.8.1 vs 4.0?

[Vasile Gaburici]

Is there a reason why JK sets the svn version of XeTeX to compile with
ICU 4.0, but TeXLive 2008 uses 3.8.1?

SVN (on Fedora 9):
Compiled with ICU version 4.0 [with modifications for XeTeX]
Compiled with zlib version 1.2.3; using 1.2.3
Compiled with FreeType2 version 2.3.7; using 2.3.7
Compiled with fontconfig version 2.5.0; using 2.5.0
Compiled with libpng version 1.2.15; using 1.2.15
Compiled with xpdf version 3.01

TeXLive 2008 (idem):
Compiled with ICU version 3.8.1 [with modifications for XeTeX]
Compiled with zlib version 1.2.3; using 1.2.3
Compiled with FreeType2 version 2.3.7; using 2.3.7
Compiled with fontconfig version 2.3.1; using 2.5.0
Compiled with libpng version 1.2.29; using 1.2.29
Compiled with xpdf version 3.02pl2