Below are the difference between Hoover UH30010com and U5140-900
Hoover U5140900 vs UH30010COM
images from manufacturer

Portable Canister Vacuum:
The UH30010COM comes with a portable canister vacuum cleaner for portable cleaning while the U5140900 does not have such a canister.

Height Adjustment:
The U5140900 has 5 manual height settings while the UH30010COM adjusts height automatically but no manual settings.

Brush Speed:
The UH30010COM has 2 speeds while the U5140900 has only 1.

Full Bag Indicator:
The UH30010COM features full bag indicator while the U5140900 does not.

Headlight:
The UH30010COM features headlight whereas the U5140900 has no headlight.

Bag Type:
The U5140900 use Allergen Media bag that can capture 99% of particles down to 5 microns.
While the U5140900 features HEPA media bag that can capture 99.97% of particles down to 0.3 microns, it gives you better air quality than allergen media bags.

Location of ON/OFF Switch:
The ON/OFF Switch on UH30010COM is on the top of the Handle whereas the one on U5140900 is located on the top left of the vacuum body.

Tools:
The UH30010COM comes with one Telescopic Extension Wand, one Crevice Tool, one Dusting Brush, one Floor brush.
Whereas the U5140900 has 2 Extension Wands, one Crevice Tool, one Dusting Brush, one Upholstery Tool.

Nozzle Width:
Nozzle Width of the UH30010COM is 14 inches while it is 15-inch on the U5140900.

Cord Length: The UH30010COM has a much longer cord.
The cord length on the UH30010COM is 35 ft while it is 25 ft on the U5140900.

Handle:
The UH30010COM features D-Shaped Handle whereas the U5140900 features Standard Grip Handle.

Weight: The UH30010COM is lighter.
The UH30010COM upright unit weighs less than 12 pounds while the U5140900 weighs more than 16 pounds.

Warranty:
The UH30010COM carries 5 year limited warranty while the U5140900 has only 1 year limited warranty.

Price: The UH30010COM is $200 more expensive than the U5140900.
UH30010COM is priced at $299.99 while the U5140900 costs $99.99 (prices checked on July 01, 2013 at hoover.com)

Color:
The UH30010COM is grey while the U5140900 is blue.

Similarities between Hoover UH30010com and U5140-900:
They are bagged upright vacuum cleaners.
equip with motorized brush but no brush On/Off switch;
12-amp motor;
no auto cord rewind.

You can also download the manuals to learn more, here are the links:
UH30010COM manual: http://hoover.com/file/537/
U5140-900 manual: http://hoover.com/file/431/

If you know more difference between Hoover UH30010com and U5140900, please share here.