Spinning is a low energy manouvre. The main issue with spinning most GA aircraft is their recovery characteristics not the intergrity of the airframe.
In both of these incidents the problem was caused by incorrect repairs/assembly and or maintenance.
I don't think it reflects in any way at all on the suitability of the C150/2 for spinning. Any other aircraft could be afflicted with a similar problem. The C150/2 airframe is very robust, I am not aware of any structural failures caused through operation in the design envelope.
I think your comparision of the C150 to a 737 is a bit flawed, just becase the C 150 is smaller it does not necessarily translate that it is less robust.
It does highlight the need for a very thorough pre flight inspection (including the full and free movements of control surfaces) before going out and doing such manouvres.