In-house attorneys around the world work varying numbers of hours each year, at least if you give credence to the combined effect of paid leave and paid public holidays mandated in each country. Consider one flagrant contrast summarized by Eduardo Porter, The Price of Everything: Solving the mystery of why we pay what we do (Portfolio/Penguin 2011) at 75: Portuguese workers get a total of thirty-five paid days off a year whereas US workers have no mandatory paid days off.
Granting in-house lawyers comparable paid time off, with such significant variance from country to country, to use 1,800 chargeable hours per year as a baseline from US law departments almost certainly overstates chargeable hours elsewhere. That distortion, for example in calculations of fully loaded costs per lawyer hour, understates the costs overseas. If lawyers in France, Germany, and the UK for example, log fewer hours, of which hours we assume the same percentage of chargeable hours as their US counterparts, then their cost to their company rises as compared to US lawyers.
The vexing question remains of what is the appropriate formula to figure out the carrying cost of internal lawyers (See my post of July 26, 2009 #1: difference it makes if you change chargeable hours; May 21, 2009: internal chargeable hours with 12 references.).
The flip side of this post, however, might be that all the technology available to in-house legal staff enables them to work from home, during the commute, and otherwise with the result that they chip in more hours than before.