  The inhomogeneities inherent to the random distribution of Sr dopants in
La_{2-x}Sr_xCuO_4 superconductors are probed by measuring the x-ray diffraction
linewidths and the Meissner transition widths, and then consistently explained
on the grounds of a simple model in which the local Sr content is calculated by
averaging over distances close to the in-plane electronic mean free path. By
taking into account these intrinsic bulk inhomogeneities with long
characteristic lengths (much larger than the superconducting coherence length
amplitudes), the precursor diamagnetism measured above Tc, a fingerprint of the
superconducting transition own nature, is then explained for all doping levels
in terms of the conventional Gaussian-Ginzburg-Landau approach for layered
superconductors. These results also suggest that the electronic inhomogeneities
observed in the normal state by using surface probes overestimate the ones in
the bulk.
