As this rule impacts on me and from speaking with Steve Young last week, I have some information about this that I got from our U.K VAT people today, which i think might clarify a little better. Perhaps... 
Imported goods: accounting for import VAT
These are normally charged at the same rate as if they had been supplied in the UK.
VAT registered businesses can account for import VAT on their VAT return by using postponed VAT accounting. Accounting for VAT on your VAT return in this way allows you to declare import VAT and reclaim it as input tax on the same VAT return. You can reclaim the VAT incurred on the imported goods you own as input tax subject to the normal rules.
Alternatively a business can choose to pay import VAT on importation. If you choose to do this, you can reclaim the VAT incurred on the imported goods you own as input tax subject to the normal rules. To claim input tax you will need the import VAT statement as evidence. A shipping or forwarding agent cannot usually reclaim this input tax because the goods were not imported to be used in part of their business.
Valuation of imported goods
The value for VAT of imported goods is their customs value, determined by the rules in Notice 252, as well as:
incidental expenses - such as commission, packing, transport and insurance costs incurred up to the goods’ first destination in the UK ;any Customs Duty or levy payable on importation into the UK; any Excise Duty or other charges payable on importation into the UK - except the VAT itself.
The value of VAT is normally added to box 22 of the import declaration automatically. If it needs to be calculated manually, you must enter the code ‘VAT’ in the rate column of box 47, and enter the value in the amount column.
As from 1st Jan commercial parcels under £135 do not incur import charges as the vat is now at the point of sale not import and the seller may have consider registering for vat in order to account for this.
Normally, if you buy parts from the USA they will charge their taxes and when you import the parts you will be charged VAT on the goods. If your not VAT registered, then postal charges on a consignment of goods under the value of £135 will not incur UK VAT.
Goods that are outside the UK at the point of sale
The seller must work out the consignment value of the goods by deciding their ‘intrinsic value’, this is the price the goods were sold for, not including: any transport or insurance costs, unless they are included in the price and not separately shown on the invoice
any other identifiable taxes and charges. Unless sent individually, the seller must add the individual values of all items in a consignment together to get the total value of the consignment.
If a seller makes changes to the value of the consignment so that its total value goes above £135 they may be liable for import VAT and Customs Duty, and have to adjust the VAT already accounted for at the point of sale.
Non VAT registered - If the goods in the USA are under the £135 (excluding USA VAT and shipping costs) then so long as they fill in the forms correctly then there is no VAT. If the cost of goods exceed that, you pay VAT on all of the costs when it comes into the UK and you can't recover the VAT.
If you register for VAT - When you purchase the goods and supply the US business with your VAT number, they charge you their taxes and shipping and when the goods arrive in the UK VAT is charged on the total cost, however you can recover the VAT on the UK import of the goods on your VAT return.
If you register for VAT then you can recover any VAT that has been charged on the import of the goods. So long as the seller completes the declaration label correctly that will show the value of the goods and you will be charged VAT accordingly.
I hope this helps a little.