Essentially, of course, it is all a question of love. Love of roots, origins, a musical habitat. Call it swing or third stream jazz if you want to, or mainstream or traditionalism. Associated with the solid precursors of the 20s, 30s and 40s with Armstrong, Benny Goodman, Bunny Berigan, Coleman Hawkins.  Or quite simply with all tunes that were written when it all happened and which long ago planted themselves, legs apart and hands on hips, in the folklore of twentieth century America.
Use which ever words you like. But don't talk about nostalgia - at least not in the mawkish sense we usually emply the term. For nostalgia - to dedicated musicians, just as to conscious listeners - remains a question of quality, not a matter of annular rings and laments for lost time.  We love Frank Sinatra, not because he imbodied middle age, suffering and transitory brilliance but because he happened to be an incomparable vocalist. We were struck dumb by Charlie Parker, not just because he belonged to the postwar era and our very own decade of the 1940s (as did so many others inferior to him) but because on his way between birth and downfall he contrived to blow a few phrases, the like of which the world had never heard.  
Nor, turning to consider this affectionate production, do we love the old songs because they are old, we love them because they are good. They were written at a time when standards were high and when imagination and harmonic inspiration still seemed inexhaustible.
Where in Stockholm should the afficionados forgather if not at Stampen, the former pawnshop in the old city, the music pub that developed into a swedish offshoot of St. Germain-des-Pres?  

Arne Domnérus, Alto Sax, Clarinet
Bengt Hallberg, Piano
Lars Erstrand, Vibes
Georg Riedel, Bass
Egil Johansen, Drums