Does the energy from ATP hydrolysis vary among different cells?
Yes, the energy from ATP hydrolysis can vary between different cell types and condition, because it depends on several factors. Hence, you will find different values in various textbooks.

First, like any chemical reaction, the free energy $\Delta G$ of ATP hydrolysis depends on the concentrations of the reactants. You can explore different values of $\Delta G$ with this calculation tool. Typical values are [ATP] = 10 mM, [ADP] = 1 mM and [P$_i$] = 20 mM, which gives $\Delta G$ = 42 kJ/mol (10 kcal/mol). But all these concentrations can vary between cells, and there is not much data available on intracellular concentrations in specific cell types. Many textbooks give free energy values denoted $\Delta G^{\circ}{'}$ which are calculated at concentrations of 1M, which is of course completely unphysiological.

In addition, the $\Delta G$ is strongly affected by the concentration of Mg$^{2+}$, because this ion associates with phosphate groups and alters their free energy. It also depends on pH, since the phosphate groups can take up/release protons. If you are interested, an in depth analysis is found here.