It should be but isn't, unless there is regulation to enforce it such as in the aviation industry, other industries are governed by market forces which usually won't pay for anything like that. The generator industry is a case in point, even though they may be providing backup power for something as critical as a hospital no one will pay for true reliability.
It's a while since I did MTBF calculations for the military and aerospace sectors but back then we could rarely get figures from manufacturers and I've no reason to believe they are any more forthcoming now. We had to use the figures from MIL Handbook 217 which is the bible of reliability prediction and is notoriously biased against anything new and unproven, I don't know what the latest issue has to say about lead free but the fact that the military and aerospace have an exemption probably says it all.
There simply isn't sufficient experience of lead free to be confident of anything and what evidence has emerged is all bad, there's a well documented but anonymous story about a very large phone company who tried to go lead free a couple of years to get some commercial advantage over their competition but had huge failure rates and was forced to go back to lead.
Information from component distributors is that most companies who are going lead free have left it very late in the hope of some sort of reprive and are now having huge problems, you can get to maybe 90% lead free components but the last 10% is very hard. There are also lots of fake lead free components on the market and if you have just one lead component on a board and put it through a wave soldering or selective soldering machine you contaminate the whole solder bath and have to throw away not only thousands of pounds worth of solder but also the bath itself as you can't clean it properly. It's going to be the last nail in the coffin of some UK firms, and for what?, WEEE is going to force the recycling of the products anyway!.