Perhaps Google is reserving for itself the right to make
hidden changes to the library itself in the future (or tightly integrated
plugins, which would still run afoul of the LGPL) to implement
digital restrictions management.
Google walks a fine line, generally preferring the corporate-friendly
"open" side of things and shunning "free". After all, their largest
deployment of all, by far, their datacenters, run a heavily modified and
nondisclosed stack, and they are immune to the requirements of the GPL
because they do not redistribute. They are violating no requirements,
but let's not confuse ourselves about where their political orientation
lies -- like all companies, it is directed first and foremost towards profit.