Macbook Air: MD232LL/A or Z0ND0002Z?
The two model numbers don't seem to refer to the exact same configuration. Model MD232LL/A appears to reference to the base model (as noted in Apple's MBA Model Identifier KB). The KB also notes: 


  If you have a custom configuration the Model Number and Configuration
  in the table may not match. Please use the Model Identifier to confirm
  the model of MacBook Air for custom configurations.


One example from Amazon - the specs include:


  
  1.8 GHz Intel Core i5 Processor
  256 GB Flash Storage
  4 GB DDR3 RAM
  


In the page from Decide.com, the specs for model Z0ND0002Z include:


  
  Core i7 2 GHz 
  8 GB RAM 
  512 GB HDD
  


It's probably that the Z0ND0002Z model is used by retailers that provide more customization, since Apple uses the MD232LL/A model in its online KB. The excerpt from the KB also supports this conclusion.