Re: Why do the cells of an onion bulb do not have any chloroplasts?

No, this has nothing to do with dead cells.  In truth the practical answer 
to this is that they don't need chloroplasts.  Think of where an onion 
lives and how much light it normally receives.  Chloroplasts only function 
in the presence of light.  Because it costs energy to develop chloroplasts, 
it is not useful for the plant to put develop them if they won't function. 
However accurate, this answer is a little simplified compared to what 
really happens.

Chloroplasts are only one type of plastid, along with chromoplasts (causing 
the red color of peppers and tomatoes) and amyloplasts (storing starch in 
potatoes and corn).  None of these plastids can be assembled from raw 
materials within the cell of a plant.  Rather they all develop from another 
type of plastid called a proplastid.  Proplastids are small and clear.  
They divide at the same time the cells divide, so every cell in a plant has 
proplastids.  However, they are difficult to see in most plants because of 
their size.  

One piece of evidence that the proplastids exist in onion cells is easily 
seen.  Leave an onion exposed to light for several days or weeks.  It will 
begin to grow new green leaves.  Also, some of the outer layers of the bulb 
(actually leaves, too), will begin to green up, as their proplastids 
develop into chloroplasts.  

According to Eames and MacDaniels (1925, p 12)
Plastids may be found in all living cells of a plant, and probably are 
present in every cell in the early stages of development.  Later they 
become restricted to certain cells, and are abundant only in those which 
have specialized functions, such as photosynthesis, storage, and color 
manifestation.  Plastids do not occur in the fungia, bacteria, …
…Plastids multiply freely by division, and in this way the large numbers 
present in some cells are in part secured.  Plastids are present in the 
very young meristematic dells where they are very minute, the smallest 
being at the limit of [light, not electron] microscopic visibility.

References:

Eames, A.J. and L.H.MacDaniels.  1925.  An Introduction to Plant Anatomy.  
McGraw-Hill Book Company, Inc:NY.  

Esau, K.  1953.  Plant Anatomy.  John Wiley And Sons, Inc:NY.

Esau, K.  1977.  Anatomy of Seed Plants, 2nd ed.  John Wiley and Sons, 
Inc:NY.