Throwing out perfectly good lovely old windows for "environmental" reasons is of course retarded; if you want more air proofing and don't already have storm windows, just get some good storms and you're done.
Replacement windows almost always uglier than good old wood windows, which architecturally fit the house and have nice wavy old glass.
Furthermore, they cannot be maintained and repaired in the same way as an old window + storm. When an IGU fails (which they do in 10-20 years typically) it cannot be repaired, it has to be replaced. Old wood windows can be easily taken a part, cleaned, resealed, and can last 100 years. (Vinyl windows and caulk and foam seal strips and so on are similarly problematic - they seem great at first, but they all decay badly in sun and weather, so have to be replaced regularly and can't really be maintained).
Replacement windows are usually shoved inside the existing window framing, and add their own thin frame which makes the opening smaller and adds an extra ugly architectural detail.
It's a standard "sustainable" bullshit corporate ripoff. To sell you some new crap and get you to throw away your perfectly good old windows. (it's like the wonderful irony of "sustainable christmas trees").
This guy addresses the issue in much more detail.