Depending on your comparison, centrifugal blowers may have tight internal clearances, or relatively liberal, clearances.  A positive displacement blower, with internal "lobes", would have very little clearance, less than .005" between rotor and housing.  Compared to the centrifugal, where the clearances are closer to .080" - .100", the centrifugal has much more clearance.  But then comparing the centrifugal to a fan where the clearances between rotor and housing can be measured in whole inches, the centrifugal has the tight clearances. 

The design of each is usually to simply convey filtered air, or gas.  Each of them do it well for their design applications.  Problems arise when the 'filtered' air contains foreign materials, moisture, and other gases, which are usually not by design.  PD's are almost never used in landfill gas applications because the filtered gas is heavily laden with moisture and particulate that never seems to be filtered out adequately. The "tight" clearances cannot handle the rust & corrosion.     

In centrifugal blowers, moisture can pass through with the air/gas, but only if the blower is always running. Once it shuts down, mother nature takes over with chemical reactions: water/rust, sulphur/sediment, and general corrosion between metals.  The corrosion starts with a simple discoloration, then a stain, and on to 'corrosion".  It builds up over time, getting thicker and thicker until it uses up all of the clearances between the rotor and casing.  When the corrosion fuses together, it will prevent the shaft from rotating.  And it can fuse strong enough so a 250 HP motor cannot budge it free!  The blower will seize up!

There are coatings that can be applied to various internal components to protect and prevent the corrosion.  Improved filtration always helps.  But in some applications, it is inevitable that the blower will eventually seize up.  Hence, "useful life" of a blower.  The blowers with the longest life are those that are always running.

Keeping the foreign material out is the best PM, but continuous monitoring will help prevent that unexpected failure.  Invest in PM, it will save you money!