i don't think they're dimples...it might be how the light is hitting the bend in the tube. anyways, you can't really judge how the frame will hold up by just the pictures. my St.Martin EVO does not have the chainstay bridge and it's absolutely the stiffest frame i've owned in 10 years. i also don't think the gussets really strengthen the frame much, i've seen many frames with gussets with cracks running alongside.