Just to be clear the spreader assembly in the picture has the welding on to a separate band.
You quite correct that welding directly onto a spar should be done carefully and with the correct materials and techniques, as the heat applied in the welding process can adversely affect the performance of the spar.
The need for a solid spreader attachment is much more important 'now days' as many rigs have a designed degree of sweep in the spreaders, and therefore the load path is somewhat less straight forward [for want of a better term] than a more 'traditional' inline spreader rig.
More of a horses for courses kind of thing, i guess.
Good discussion.
Regards
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